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Occurrence Model for Volcanogenic Beryllium Deposits
Chapter F of
Mineral Deposit Models for Resource Assessment
Scientific Investigation Report 2010–5070–F
U.S. Department of the Interior
U.S. Geological Survey
COVER. Sample of large layered nodule from the Roadside pit showing fluorite, opal, and
bertrandite mineralization. The nodule has an interior of fine-grained quartz, fluorite, and opal, an
intermediate zone of black chalcedonic quartz, and an outer zone of white opal with minor fluorite.
Beryllium is concentrated in the outer opal-fluorite zone; such samples can contain as much as
1-percent beryllium as bertrandite. Size of the sample is 16×12 centimeters (photograph by David A.
Lindsey, Emeritus, U.S. Geological Survey).
Occurrence Model for Volcanogenic
Beryllium Deposits
By Nora K. Foley, Albert H. Hofstra, David A. Lindsey, Robert R. Seal, II,
Brian Jaskula, and Nadine M. Piatak
Chapter F of
Mineral Deposit Models for Resource Assessment
Scientific Investigation Report 2010–5070–F
U.S. Department of the Interior
U.S. Geological Survey
U.S. Department of the Interior
KEN SALAZAR, Secretary
U.S. Geological Survey
Marcia K. McNutt, Director
U.S. Geological Survey, Reston, Virginia: 2012
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Suggested citation:
Foley, N.K., Hofstra, A.H., Lindsey, D.A., Seal, R.R., II, Jaskula, Brian, and Piatak, N.M., 2012, Occurrence model for
volcanogenic beryllium deposits, chap. F of Mineral deposit models for resource assessment: U.S. Geological Survey
Scientific Investigations Report 2010–5070–F, 43 p.
iii
Contents
Abstract ...........................................................................................................................................................1
Introduction.....................................................................................................................................................1
Overview.................................................................................................................................................1
Scope and Purpose ..............................................................................................................................3
Deposit Type and Associated Commodities ..............................................................................................3
Name.... ...................................................................................................................................................3
Synonyms ...............................................................................................................................................3
Brief Description ...................................................................................................................................5
Associated Deposit Types ...................................................................................................................6
Fluorite Breccia Pipe Deposits ..................................................................................................6
Carbonate-Hosted Epithermal Beryllium Deposits ................................................................6
Volcanogenic Uranium Deposits ...............................................................................................6
Gem Beryl Deposits .....................................................................................................................8
Beryllium-Fluorine Skarn-Greisen Deposits ............................................................................8
Primary and Byproduct Commodities .......................................................................................9
Example Deposits..................................................................................................................................9
Metallogenic Provinces and Epochs ...............................................................................................10
Historical Evolution of Descriptive and Genetic Knowledge and Concepts ......................................10
Regional Environment .................................................................................................................................11
Geotectonic Environment ..................................................................................................................11
Geologic Setting of Spor Mountain Deposits ........................................................................12
Duration of the Magmatic-Hydrothermal System and Mineralizing Processes ......................16
Duration of Spor Mountain System ........................................................................................16
Relations to Structures ......................................................................................................................16
Relations to Igneous Rocks ...............................................................................................................17
Relations to Sedimentary Rocks ......................................................................................................17
Relations to Metamorphic Rocks .....................................................................................................17
Physical Description of Deposit ................................................................................................................17
Deposit Dimensions ............................................................................................................................17
Structural Setting(s) and Controls ...................................................................................................18
Geophysical Characteristics .............................................................................................................18
Hypogene Ore and Gangue Characteristics ...........................................................................................18
Mineralogy and Mineral Assemblages ...........................................................................................18
Paragenesis .........................................................................................................................................20
Zoning Patterns ...................................................................................................................................22
Hydrothermal Alteration .............................................................................................................................22
Argillic and Feldspathic Alteration ..................................................................................................23
Kaolinitization ......................................................................................................................................24
Supergene Ore Characteristics and Processes .....................................................................................24
Geochemical Characteristics ....................................................................................................................25
Trace Elements and Element Associations ....................................................................................25
Zoning Patterns ...................................................................................................................................25
Fluid-Inclusion Microthermometry ..................................................................................................25
iv
Stable Isotope Geochemistry ...........................................................................................................25
Radiogenic Isotope Geochemistry of Ore .......................................................................................25
Depositional Process .........................................................................................................................26
Petrology of Associated Igneous Rocks ..................................................................................................27
Petrology of Associated Sedimentary Rocks ..........................................................................................28
Petrology of Associated Metamorphic Rocks ........................................................................................29
Theory of Deposit Formation ......................................................................................................................29
Sequence of Events ............................................................................................................................29
Genetic Model .....................................................................................................................................29
Geoenvironmental Features and Anthropogenic Mining Effects ........................................................32
Weathering Processes ......................................................................................................................32
Pre-Mining Baseline Signatures in Soil, Sediment, and Water ..................................................33
Past and Future Mining Methods and Ore Treatment ..................................................................33
Volume of Mine Waste and Tailings ................................................................................................33
Mine Waste Characteristics .............................................................................................................33
Chemistry.....................................................................................................................................33
Mineralogy ..................................................................................................................................35
Acid-Base Accounting ..............................................................................................................35
Element Mobility Related to Mining in Groundwater and Surface Water.................................35
Ecosystem Issues ...............................................................................................................................35
Human Health Issues .........................................................................................................................35
Climate Effects on Geoenvironmental Signatures ........................................................................36
Exploration and Resource Assessment Guides ......................................................................................36
Acknowledgments .......................................................................................................................................36
References Cited..........................................................................................................................................36
Figures
1. Map showing the general locations of beryllium resources referred to in
the report........................................................................................................................................2
2. A generalized cross section showing geologic setting and example deposits
for the major types of beryllium (Be) resources associated with metaluminous
and weakly peraluminous magma systems and the relation of volcanogenic Be
deposits such as Spor Mountain, Utah, to other types of Be deposits that are
associated with magmas of this general composition ...........................................................4
3. Diagram showing beryllium oxide (BeO) concentrations (weight percent) and
tonnages (Mt, million metric tons) for volcanogenic Be and selected carbonatehosted epithermal replacement, skarn, and pegmatite deposits .........................................5
4. Generalized index map showing locations of features of the Thomas Range,
Utah, as referred to in the report ...............................................................................................8
5. Geologic map of Spor Mountain area, Utah...........................................................................13
6. Photographs of beryllium tuff and rhyolite flow members of Spor Mountain
Formation .....................................................................................................................................14
v
7. Histograms showing fluorine (F) and beryllium (Be) contents of melt inclusions
in quartz phenocrysts from Spor Mountain beryllium tuff and a crosscutting
21.56-Ma intrusive plug..............................................................................................................16
8. Photographs of (A) Nodule from Roadside pit with an interior of quartz, opal, and
fluorite and an outer zone of opal and fluorite that contains as much as 1-percent
beryllium as bertrandite. (B) Nodule from Roadside pit with an interior of graybrown calcite, an intermediate zone of black chalcedonic quartz, and an outer
zone of white opal with minor fluorite. (C) Fluorite-opal nodule from Monitor
prospect yielded uranium/lead ages of ≈20.8 Ma (fluorite-opal core), ≈13 Ma
(white opal middle zone), and ≈8 Ma (translucent opal rim) ...............................................19
9. Photographs of (A) Siliceous shells and detritus in calcium-carbonate relic
matrix being replaced by later fluorite mineralization. (B) Elemental maps by
electron microprobe analysis for calcium (Ca), silicon (Si), magnesium (Mg),
and fluorine (F) confirm that magnesium is completely stripped from the
carbonate leaving a mix of mainly calcite and siliceous materials ...................................20
10. Photographs showing textures typical of ore samples of volcanogenic beryllium
deposits ........................................................................................................................................21
11. Photographs showing (A) Late fluorite and chalcedony in vug rimmed by
manganese oxide minerals. (B) Purple fluorite and late quartz in vug ..............................21
12. Diagram showing generalized paragenetic sequence for beryllium-ore nodules
of the Spor Mountain district ....................................................................................................21
13. Diagram showing simplified reaction paths models for the formation of fluorite
replacement front in beryllium ore nodules ...........................................................................27
14. Diagram showing a general model for formation of volcanogenic deposits of uranium,
beryllium, and other lithophile elements.................................................................................30
15. Diagrams showing minimum volumes of tuff or pluton required to form beryllium (Be)
resource at Spor Mountain .......................................................................................................31
16. Plot showing extraction efficiency (percent) versus volume (million m3) .........................31
17. Diagram showing the solubility of bertrandite and the dominant speciation of
dissolved beryllium (Be) as a function of log aBe2+ and pH at 25°C ...................................33
Tables
1. Deposits and occurrences considered in developing the volcanogenic epithermal
beryllium (Be) deposit model ......................................................................................................7
2. Types of nonpegmatitic beryllium (Be) occurrences ............................................................10
3. Geochemical comparison of anorogenic granites and topaz rhyolites.............................11
4. Chemical compositions of topaz rhyolite and melt components in the vicinity of
Spor Mountain beryllium district..............................................................................................15
5. Mineralogy and chemical composition of unmineralized (vitric) and mineralized
tuff, Spor Mountain and Thomas Range, Utah.......................................................................23
6. A model hydrothermal fluid composition for Spor Mountain ..............................................26
7. Geochemical characteristics (dissolved) of groundwater in the vicinity of the
Spor Mountain deposit, Utah ....................................................................................................34
8. Environmental guidelines relevant to Spor Mountain beryllium deposits ........................34
Occurrence Model for Volcanogenic Beryllium Deposits
By Nora K. Foley, Albert H. Hofstra, David A. Lindsey, Robert R. Seal, II, Brian Jaskula, and Nadine M. Piatak
Abstract
Current global and domestic mineral resources of beryllium (Be) for industrial uses are dominated by ores produced
from deposits of the volcanogenic Be type. Beryllium deposits
of this type can form where hydrothermal fluids interact with
fluorine and lithophile-element (uranium, thorium, rubidium,
lithium, beryllium, cesium, tantalum, rare earth elements, and
tin) enriched volcanic rocks that contain a highly reactive
lithic component, such as carbonate clasts. Volcanic and hypabyssal high-silica biotite-bearing topaz rhyolite constitutes
the most well-recognized igneous suite associated with such
Be deposits. The exemplar setting is an extensional tectonic
environment, such as that characterized by the Basin and
Range Province, where younger topaz-bearing igneous rock
sequences overlie older dolomite, quartzite, shale, and limestone sequences. Mined deposits and related mineralized rocks
at Spor Mountain, Utah, make up a unique economic deposit
of volcanogenic Be having extensive production and proven
and probable reserves. Proven reserves in Utah, as reported
by the U.S. Geological Survey National Mineral Information Center, total about 15,900 tons of Be that are present in
the mineral bertrandite (Be4Si2O7(OH)2). At the type locality
for volcanogenic Be, Spor Mountain, the tuffaceous breccias
and stratified tuffs that host the Be ore formed as a result of
explosive volcanism that brought carbonate and other lithic
fragments to the surface through vent structures that cut the
underlying dolomitic Paleozoic sedimentary rock sequences.
The tuffaceous sediments and lithic clasts are thought to make
up phreatomagmatic base surge deposits. Hydrothermal fluids
leached Be from volcanic glass in the tuff and redeposited the
Be as bertrandite upon reaction of the hydrothermal fluid with
carbonate clasts in lithic-rich sections of tuff. The localization
of the deposits in tuff above fluorite-mineralized faults in carbonate rocks, together with isotopic evidence for the involvement of magmatic water in an otherwise meteoric water-dominated hydrothermal system, indicate that magmatic volatiles
contributed to mineralization. At the type locality, hydrothermal alteration of dolomite clasts formed layered nodules
of calcite, opal, fluorite, and bertrandite, the latter occurring
finely intergrown with fluorite. Alteration assemblages and
elemental enrichments in the tuff and surrounding volcanic
rocks include regional diagenetic clays and potassium feldspar
and distinctive hydrothermal halos of anomalous fluorine,
lithium, molybdenum, niobium, tin, and tantalum, and intense
potassium feldspathization with sericite and lithium-smectite
in the immediate vicinity of Be ore. Formation of volcanogenic Be deposits is due to the coincidence of multiple factors
that include an appropriate Be-bearing source rock, a subjacent
pluton that supplied volatiles and heat to drive convection of
meteoric groundwater, a depositional site characterized by the
intersection of normal faults with permeable tuff below a less
permeable cap rock, a fluorine-rich ore fluid that facilitated Be
transport (for example, BeF42– complex), and the existence of a
chemical trap that caused fluorite and bertrandite to precipitate
at the former site of carbonate lithic clasts in the tuff.
Introduction
Overview
Current global and domestic mineral resources of beryllium (Be) are dominated by ores produced from volcanogenic
Be deposits, and this deposit type can be viewed as a subset
of the general class of nonpegmatitic, igneous-associated Be
deposits (for example, Barton and Young, 2002 and references therein). Overall, world resources of Be are estimated
to be more than 80,000 metric tons (beryl equivalents), and
65 percent of this is in deposits in the United States (fig. 1),
primarily from those in volcanogenic Be deposits of western
Utah and Be skarn, hydrothermal replacement, and greisen
deposits of the Seward Peninsula of Alaska (Alexsandrov,
2010; Sainsbury, 1964), which indicates that the world’s current major reserves of Be are nonpegmatitic (Jaskula, 2010).
Global production of Be in 2010 was estimated at 190 metric
tons Be of which the United States accounted for more than
85 percent. Lesser producers (fig. 1) include China (Changning City, Hunan Province; Fuyun County, Xinjiang Uygur
Autonomous Region), Mozambique (Zambezia Province),
Madagascar (Ankazobe, Analamanga, Antananarivo Province), and Portugal (Viseu, Centro Region). The Yermakovskoye (Ermakovska) Be deposit in the Siberian Republic of
Buryatiya is currently in the development stage with construction of a Be processing plant; the mine is planned to operate at
capacity by 2017.
2
Occurence Model for Volcanogenic Beryllium Deposits
Lost River, Alaska
Seward
Peninsula
Tanco pegmatite,
Manitoba
Spor Mountain, Utah
Honey Comb Hills, Utah
Wah Wah Mountains, Utah
North Carolina
pegmatites
Apache Warm Springs, New Mexico
Sierra Blanca,Texas
Aguachile, Mexico
Mascusani, Peru
Minas Gerais,
Brazil
MERCATOR PROJECTION
Central Gobi volcanic belt, Teg-Ula, Mongolia
Xinjiand Uygur
Autonomous Region
Western Transbaikal,
Republic of Buryatiya,
Yermakovskoye
Orot
Portugal,
Viseu,
Centro Region
Far East Sn-F-Be
Changning City
Hunan Province,
China (skarn)
Shixi, Zhejiang
Southeast China
Zambezia Province,
Mozambique
Brockman
Antananarivo Province,
Madagascar pegmatites
Figure 1.
Western
Australia
Map showing the general locations of beryllium resources referred to in the report.
Deposit Type and Associated Commodities
The Be ores constitute the principal global resource of
Be for computer, telecommunication, aerospace, defense,
and nuclear industries. Beryllium is used to produce light and
very strong alloys, metallic glasses, thin foils, and mirrors.
Beryllium alloys are used mostly in applications in aerospace,
automobile, and computer technologies; oil and gas drilling equipment; musical instruments; medical devices, and
telecommunications (for example, Materion Corporation,
2011). Beryllium glasses and foils are used in X-ray imaging
and detector applications and Be mirrors are used in satellites and telescope optics and in optical guidance systems. In
addition, Be salts are used in fluorescent lamps, X-ray tubes,
and as a deoxidizer in bronze metallurgy. The uses of Be in
applications for which its properties are crucial are expected
to expand rapidly with technological advances (Tomberlin,
2004). For example, if a viable manufacturing process is
developed, nuclear fuel containing Be and uranium oxides
may prove to be longer lasting, more efficient, and safer than
conventional nuclear fuels (Kim, 2010). The cost of Be is high
relative to that of other materials, including uranium, and,
in some applications, metal matrix or organic composites,
high-strength grades of aluminum, pyrolytic graphite, silicon
carbide, steel, or titanium may be substituted for Be metal or
composites. For example, in some applications copper alloyed
with Ni-Si, Sn, Ti, or Sn-P may be substituted for berylliumcopper alloys and aluminum or boron nitride may be substituted for Be oxide, although these substitutions can result in
substantially reduced performance.
Scope and Purpose
This report is part of an effort by the U.S. Geological
Survey (USGS) to update existing mineral deposit models
and to develop new descriptive models for use in upcoming national and regional mineral resource assessments; the
models are a necessary component of the current USGS
assessment methodology (see for example, Singer and Berger,
2007). This general occurrence model is intended to provide a
description of the characteristics of volcanogenic Be deposits,
such as those found at Spor Mountain, Utah (fig. 1), which
is the dominant resource for domestic Be production. This
occurrence model can be used for the identification and assessment of undiscovered Be deposits of this type. The occurrence model highlights the distinctive aspects and features
of volcanogenic Be deposits that pertain to the development
of assessment criteria and puts forward a baseline analysis
of the geoenvironmental consequences of mining deposits of
this type. Significant papers upon which the volcanogenic Be
deposit model described herein is based include Lindsey and
others (1973, 1975), Lindsey (1975, 1977, 1979a,b, 1982,
1998, 2001), Burt and Sheridan (1981, 1982), Christiansen
and others (1983, 1984), Ludwig and others (1980), Wood
(1992), and Barton and Young (2002). Many of these works
build on basic concepts used in categorizing genetic types of
Be deposits as discussed in Beus (1966).
3
Deposits included in this model are economically
significant end-members in a group of Be-rich deposit types
that form in lithophile-element-enriched volcano-plutonic
centers where hydrothermal fluids interact with carbonate rock
sequences (fig. 2). To provide a coherent basis for assessing
the probability of the occurrence of economic deposits of the
type exemplified by deposits at Spor Mountain, Utah, the
ore deposit model presented here is restricted in application.
This model does not apply to Be skarn, greisen, and replacement deposits that are hosted primarily by carbonate-bearing
sedimentary rock sequences intruded by Be-bearing igneous
rocks, although they are related by mineralogy and process.
Beryllium skarn and greisen deposits, which form by intrusion
of granite or rhyolite laccoliths, stocks, or dikes into carbonate rock and concomitant metasomatic replacement processes
can have phenakite, bertrandite, and helvite group minerals,
and less commonly, bavenite, leucophanite, gadolinite, and
milarite (Grew, 2002; Barton and Young, 2002, and references
therein). They often display a distinctive texture of rhythmically banded replacements containing alternating light and
dark layers of fluorite, Be minerals (helvite-danalite is typical), silicates, and magnetite. Carbonate replacement deposits
have distinctly different resource assessment characteristics.
Examples of this model include Be deposits of the Seward
Peninsula, Alaska.
This model also does not apply to Be deposits hosted
by intrusive igneous rocks, for example pegmatite deposits,
because those deposits have different petrologic and crystallization histories (Barton and Young, 2002, and references
therein). Greater depths of emplacement, higher temperatures,
and a source region that constrains the evolution of bulk and
melt chemistries result in distinctly different mineralogical
attributes and thus economic potential. Well-documented
examples of this type have beryl as the primary Be phase.
The format and organization of this report follows a general template designed for use in the USGS mineral resource
assessment project that ensures the consistent and systematic
inclusion of information related to the occurrence of a broad
suite of mineral commodities and deposit models.
Deposit Type and Associated
Commodities
Name
Volcanogenic Be type
Synonyms
A number of names have been formally and informally
applied to deposits of this type. They include volcanic-hosted
epithermal Be, epithermal Be deposits, hydrothermal Be,
replacement Be, volcanogenic epithermal Be, Be tuff deposits,
and Spor Mountain Be.
4
Occurence Model for Volcanogenic Beryllium Deposits
Be Environments Associated with Metaluminous and Weakly
Peraluminous Systems
Red beryl in gas cavities and cooling joints
(Wah Wah, Utah; Black Range, N. Mex.)
Be-enriched magma
(Thomas Range, Utah)
Replacement Be-minerals in
tuff (Spor Mountain, Utah)
Replacement Be-minerals in
carbonate (Sierra Blanca, Tex.)
Fe-rich skarns and replacements ± porphyry-style
Mo (-W) (Iron Mountain, N. Mex.;
Oslo Graben, Norway) (Ermakovka, Siberia)
Miarolitic pegmatites and greisen
quartz veins (Mt. Antero, Colo.;
Sheeprock, Utah)
Greisen Sn (-Ta-Nb-Zn)
(Younger Granites, Nigeria and Niger)
EXPLANATION
Rock Types
Mineralization styles
Rhyolite lavas and pyroclastic
tuff deposits
Magmatic enrichments (dispersed in minerals or
volcanic glass)
Subvolcanic intrusions,
domes, caldera structures
Miarolitic and pegmatitic zones (Alpine type clefts or
pegmatites in metamorphic rocks
Granites, syenites,
porphyry-style intrusives
High-temperature (>300˚C) veins, individual, sheeted
and stockwork
Paleozoic sedimentary
sequences, platform
carbonates
Low-temperature (<300˚C) veins, mostly individual or
sheeted
Skarns, typically F-rich with variable Al-Fe-metal
contents
Carbonate replacement deposits, typically F-rich
Figure 2. A generalized cross section showing geologic setting and example deposits for the major types of beryllium (Be)
resources associated with metaluminous and weakly peraluminous magma systems and the relation of volcanogenic Be
deposits such as Spor Mountain, Utah, to other types of Be deposits that are associated with magmas of this general
composition. Modified from Barton and Young (2002).
Deposit Type and Associated Commodities
Brief Description
Geological, mineralogical, and geochemical data summarized in this model are intended to be used to aid in
identification of tracts of land permissive for the occurrence
of volcanogenic epithermal Be deposits, such as those found
at Spor Mountain. The deposits at Spor Mountain constitute a
globally significant resource of volcanogenic Be (fig. 3) having produced from 1969 to 2009 almost 5,000 metric tons of
recovered Be and containing proven and probable reserves in
2009 of ≈10 million tons of ore at a grade of 0.266 weight percent Be (McLemore, 2010a; Brush Engineered Materials, Inc.,
2009). For comparison, figure 3 shows grade and tonnage data
for volcanogenic Be deposits with selected data for pegmatite
deposits, skarns, and carbonate-hosted epithermal deposits.
The following description is summarized from Barton and
Young (2002) and references therein; original sources are cited
in later section.
Volcanogenic Be deposits are hosted by metaluminous
to peraluminous rhyolite in which carbonate lithic fragments
in tuffaceous volcaniclastic rocks were replaced by fluorite,
bertrandite, and other silicate minerals. Deposit origin is
primarily the result of igneous processes that lead to the concentration of fluorine and Be in rhyolite melts. Post-magmatic
processes also play an important role in the deposits because
they cause redistribution and significant localized enrichment
of Be to form high-grade ore. These deposits form where
hydrothermal fluids interact with lithophile-element-enriched
volcanic rocks that contain a highly reactive lithic component,
such as carbonate clasts. Host rocks are typically volcanic
and subvolcanic (hypabyssal) high-silica biotite-bearing topaz
rhyolite and related tuffs and ash flows, although granite
porphyry may be present. Together these rocks compose the
fluorine-rich igneous suites that are associated with volcanogenic Be deposits. The exemplar setting is an extensional
tectonic environment where younger topaz-bearing igneous
rock sequences overlie older dolomite, quartzite, shale, and
limestone sequences. At the type locality at Spor Mountain,
the tuffaceous breccias and stratified tuffs containing Be ore
formed as a result of explosive fluorine- and lithophile-rich
volcanism that brought ash, carbonate fragments, and other
lithics to the surface through vent structures through underlying Paleozoic dolomite rock sequences. The tuffaceous sediments and carbonate lithic clasts make up the volcaniclastic
phreatomagmatic base surge deposits. Hydrothermal fluids are
thought to have leached Be and other elements from volcanic
glass in the tuff and concentrated the Be as bertrandite when
the hydrothermal fluid reacted with carbonate in lithic-rich
sections of tuff. Hydrothermal alteration of dolomite clasts
formed layered nodules of calcite, opal, and fluorite. The
principal Be-ore mineral, bertrandite, occurs solely as submicroscopic grains admixed with fluorite. Alteration assemblages and elemental enrichments in the tuff and surrounding
volcanic rocks include regional diagenetic clays and potassium
(K) feldspar, and, in the vicinity of Be ore, distinctive halos
of F, Li, Mo, Nb, Ta, and Sn, and intense potassium feldspathization, sericite, and lithium smectite. The size and grade of
a deposit is thought to relate to the distribution of carbonate
lithic-rich zones in host tuff and the duration and efficiency of
the mineralizing hydrothermal system.
10
Figure 3. Beryllium oxide (BeO)
concentrations (weight percent) and
tonnages (Mt, million metric tons)
for volcanogenic Be and selected
carbonate-hosted epithermal
replacement, skarn, and pegmatite
deposits. Modified from Barton and
Young (2002), McLemore (2010a), and
this study. Ppm, parts per million.
Sierra Blanca,
Tex.
1
Yermakovskoye,
Siberia
BeO (weight %)
Warm Springs,
N. Mex. Tanco,
Manitoba,
Canada
0.1
Spor Mountain, Utah
Lost River,
Alaska
Aguachile, Mexico
All of North
Carolina
Brockman,
Australia
0.01
nta
Co
Pegmatite
0.01
0
0.0001
0.001
10
Skarns
d
ine
0.1
1
Size (metric ton)
m
O(
Be
s)
ton
4
Carbonate-hosted
epithermal Be
ic
etr
10
2
10
0.001
EXPLANATION
Be models
Volcanogenic Be
Hypothetical
Be-bearing magma0.4 km3 @ 3.6 ppm Be
estimated by Barton and Young,
2002)
10
5
100
1000
6
Occurence Model for Volcanogenic Beryllium Deposits
Associated Deposit Types
Topaz-bearing rhyolites, such as those associated with
volcanogenic Be deposits, are of resource significance for a
wide range of additional rare-metal commodities in a variety
of deposit types (Kovalenko and Kovalenko, 1976; Kovalenko and others, 1979; Burt and others, 1982; Ludington
and Plumlee, 2009; Nash, 2010). Their established economic
importance includes (1) volcanogenic deposits of Be, U, Sn,
and fluorite, (2) fluorite- and silver-rich base metal ores, and
(3) topaz-rich porphyry molybdenum ± tungsten deposits of
the Climax and Henderson type (Kamilli and others, in press).
Fluorine-rich rhyolites that host volcanogenic Be deposits
can also be associated with elevated and potentially economic
concentrations of thorium, niobium, and rare earth elements
(REE); for example, at the Brockman deposit of Western
Australia, the informally named Niobium tuff contains proven
reserves of ≈4.3 million metric tons (Mt) of rare metals
including 0.44-percent Nb2O5 and ≈50–1,500 parts per million
(ppm) Be (see table 1 for details and other examples).
Deposit types found in close spatial association with the
volcanogenic Be deposits at Spor Mountain include (1) breccia
pipe fluorite1 deposits, (2) carbonate-hosted Be deposits,
(3) volcanogenic uranium, and (4) fumarolic gem beryl
deposits. These four deposit types are expected to be the most
typically associated deposit models for volcanogenic Be. An
exception is for fluorine-rich igneous suites dominated by
porphyry intrusions or plugs; in such systems Be skarns and
greisen deposits containing calc-silicate minerals may also be
present. The short descriptions below are compiled from
references listed in table 1.
Fluorite Breccia Pipe Deposits
Deposits of fluorite in the Spor Mountain district have
been described by Staatz and Osterwald (1959), Staatz and
Carr (1964), and Bullock (1981). Commercial fluorite production at Spor Mountain began in 1944 from massive deposits of
fluorite occurring as cements in breccias pipes, in veins, and
as disseminations that are associated with shattered zones in
dolomite at the intersection of faults and vent-related explosive features. The fluorite ore contains 60–90 percent fluorite
and is generally uraniferous; a purple color is indicative of
uranium. The fluorite mainly occurs as soft powdery masses
in dense aphanitic boxwork forms. Unusual forms of purple
acicular fluorite with radiating needles in massive fluorite
and opaline silica are present in some fluorite pipes suggesting complex replacements of early-formed minerals. These
fluorite deposits contain no detectable Be. No fluorite is currently being produced in the Spor Mountain district. At other
volcanogenic Be deposits that lack significant carbonate rock,
for example the Honey Comb Hills, Utah, deposit, fluorite is
1
These are referred to as fluorspar deposits in older literature. Fluorite is
the preferred term for the principal ore of fluorine; fluorspar is considered
obsolete (AGI, 2012).
only present as minor replacements as stringers and veinlets
in tuff, and as such does not form economic concentrations.
In comparison, near the Aguachile carbonate replacement
Be deposits of Coahuila, Mexico, sizeable fluorite replacement deposits (≈1 Mt) occur in chimneys, veins, and contactlocalized masses in brecciated zones in limestone near rhyolite
porphyry dikes. The fluorite is fine-grained, botryoidal, and
generally contains less than 20 ppm Be (Kesler, 1977).
Carbonate-Hosted Epithermal Beryllium Deposits
A number of small and irregularly shaped, Be-rich zones
are located in carbonate rocks stratigraphically beneath the
bedded tuff that hosts volcanogenic Be ores at Spor Mountain.
These uneconomic Be occurrences are in Paleozoic sequences
of the Sevy Dolomite and Lost Sheep Member of Laketown
Dolomite.
More significant carbonate-hosted Be deposits are
associated with subvolcanic rhyolite at Aguachile, Mexico,
and Sierra Blanca, Tex. The beryllium-fluorine mineralization at Aguachile occurs as replacements and void fillings
in brecciated limestone intruded by rhyolite (subvolcanic)
porphyry of a peraluminous character (Simkins, 1983; Kesler,
1977; McLemore, 2010a), although the related igneous suite
is reportedly peralkaline in bulk composition (McAnulty and
others, 1963). Bertrandite is present with calcite and quartz in
fluorite-rich deposits in limestone intruded by a rhyolite dike
near the ring fault of a caldera, and the principal ore body has
approximately 0.3-percent beryllium oxide (BeO) (Kesler,
1977). The igneous rocks provided the bulk of the fluorine,
and the limestone provided calcium; deposition was caused
by change in pH (Kesler and others, 1983). At Sierra Blanca,
western Texas, Be-rich fluorite deposits occur in association
with peralkaline-metaluminous volcanic rock sequences. The
Be deposits occur within Cretaceous limestones beneath an
intrusive contact with an overlying rhyolite laccolith. The
rhyolite laccoliths of Sierra Blanca are strongly peraluminous
and have anomalous beryllium and fluorine contents (Rubin
and others, 1987, 1988, 1990). The alkaline rhyolites are also
cryolite-bearing and contain elevated amounts of Be, Li, Nb,
Rb, REE, Th, Y, and Zn .
Volcanogenic Uranium Deposits
Deposits of this type form near centers of eruption and
more distal as a result of deposition of ash with leachable uranium (Nash, 2010). Hydrothermal fluids remove uranium from
uranium-bearing silicic volcanic rocks (typically >10 ppm
uranium) and concentrate it at sites of deposition within veins,
stockworks, breccias, volcaniclastic rocks, and lacustrine
caldera sediments (Breit and Hall, 2011). Immediately east of
Spor Mountain, uranium was discovered in 1953 at the Yellow
Chief deposit (Bowyer, 1963; Staatz and Carr, 1964; Lindsey,
1978, 1981). Production from 1959 to 1962 was 191 tons
of U3O8 at 0.20-percent U3O8 mainly from beta-uranophane
Deposit Type and Associated Commodities
Table 1.
Deposits and occurrences considered in developing the volcanogenic epithermal beryllium (Be) deposit model.
[Data summarized primarily from Barton and Young (2002, their appendix A); Mt, million metric tons; kT, kiloton; Ma, million years ago; ppm, parts
per million]
Age of complex/
volcanic unit/
mineralization
Brief description of occurrence and contained
Be ore
Primary data references
Bertrandite in fluorite-silica replacement of carbonate clasts in lithic tuff (7 Mt at 0.72% BeO),
extensive Li-Zn-bearing K-feldspar and clay
alteration; overlying 6–7 Ma topaz rhyolites
have red beryl
Griffitts, 1964; Shawe, 1966,
1968; Lindsey and others, 1973;
Lindsey, 1977; Ludwig and
others, 1980; Burt and Sheridan,
1981; Baker and others, 1998
Honey Comb Hills/ Middle Cenozoic
Utah, U.S.A.
Be in fluorite-silica replacements, stringers, veinlets in tuff
Montoya and others, 1964;
McAnulty and Levinson, 1962
Wah Wah Mountains/Utah,
U.S.A.
Middle Cenozoic/
≈23 Ma
Topaz rhyolite with late red beryl + kaolinite in
fractures with early Mn-Fe oxides; main gem
red beryl source
Keith and others, 1994; Thompson
and others, 1996
Apache Warm
Springs/Socorro
County, New
Mexico, U.S.A.
Bertrandite in small quartz veins and stringers in
Middle Cenozoic/
fractures and disseminations in rhyolite and
≈28 Ma/≈<28–
rhyolite ash-flow tuff, intense acid-sulfate
>24.4 Ma, bracketalteration
ed by stratigraphy
McLemore, 2010a,b and references therein; Shawe, 1966;
Hillard, 1969; Be Resources,
Inc. at http://www.beresources.
com; accessed December 10,
2011
Aguachile/
Coahuila,
Mexico
Middle Cenozoic/
≈28 Ma
Bertrandite-adularia-bearing fluorite replacement
(17 Mt at 0.1% BeO)
adjacent to alkaline rhyolite and riebeckite
quartz syenite
Levinson, 1962; McAnulty and
others, 1963; Griffitts and
Cooley, 1978; Simpkins, 1983
Sierra Blanca/
Texas, U.S.A.
Middle Cenozoic/
36.2 Ma/coeval
with intrusion
Fluorite-rich replacement bodies in limestone
adjacent to Li-Be-Zn-Rb-Y-Nb-REE-Th-rich
alkaline cryolite-bearing
rhyolites; 850 kT at 1.5% BeO as bertrandite,
phenakite (behoite, berborite, chrysoberyl);
minor grossularitic skarn; clays + analcime
McAnulty and others,1963; Price
and others, 1990; Rubin and
others, 1987, 1988, 1990;
Henry, 1992
Deposit/
occurrence
Spor Mountain/
Utah, U.S.A.
Middle Cenozoic/
≈21 Ma/≈21 Ma
and younger
Northern Basin and Middle Cenozoic/
Miocene
Range Province/
Oregon, Idaho,
Nevada, Utah,
and California,
U.S.A.
Mainly western Utah Be belt; most occurrences in Warner and others, 1959; Shawe,
1966; Lindsey, 1977; Burt and
volcanic rocks, but also skarn (helvite-beryl) and
Sheridan, 1986; Congdon and
granite-hosted occurrences—dominant Be
Nash, 1991
producer; magmas up to 80 ppm Be
Andean Altiplano/
Macusani, Peru
Middle Cenozoic/
Miocene (4.2 Ma;
9.3 Ma)
Beryllium minerals apparently rare, but widespread. Miocene rare-metal-enriched felsic
intrusive and volcanic centers, many with SnAg-(±B) ores, fluorite is relatively uncommon;
Macusani tuff
Pichavant and others, 1988a,b;
Lehmann and others, 1990;
Dietrich and others, 2000;
Noble and others, 1984
Transbaikal/
eastern
Mongolia
Teg-Ula
Mesozoic
Many deposit types associated with mainly Mesozoic granitoids ranging from peraluminous to
peralkaline; volcanic-hosted Be in Mongolia
Kovalenko and Yarmolyuk 1995;
Kremenetsky and others, 2000;
Reyf and Ishkov, 2006; Lykhin
and others, 2010
Shixi/ Zhejiang,
South China
Mesozoic?
Hypabyssal dikes of porphyritic sodic rhyolite, albitized and sercitized, high Be (as helvite, beryl,
bertrandite, and euclase) and Nb, Ta, Zr, F
Lin, 1985
Brockman/Western
Australia
Paleoproterozoic/
1870 Ma
Hydrothermally altered fluorite-bearing alkali
rhyolite with Nb-Zr-REE-Ta-Be enrichment
(4.3 Mt at 0.08% BeO); predates orogenesis
Ramsden and others, 1993; Taylor
and others, 1995a,b
7
8
Occurence Model for Volcanogenic Beryllium Deposits
(Ca(UO2)2(SiO3OH)2.5H2O) occurring in bed-parallel lenses
in volcanic sandstone and conglomerate that directly underlie
21-Ma tuff and rhyolite. At the Yellow Chief mine, secondary
uranium minerals make up tabular lenses of ore in the tuffaceous rocks. A small amount of uranium was also produced
(no data reported) from the Apache Warm Springs, N. Mex.,
deposit (Hillard, 1969).
Gem Beryl Deposits
Rare gem-quality red beryl occurs in miarolitic cavities in
topaz rhyolite (Keith and others, 1994; Thompson and others,
1996; and Christiansen and others,1997). Such gem deposits
are likely to occur in vesicular lavas found in volcanogenic
Be environments. At Spor Mountain, the strongly colored
manganese-rich beryl is restricted in occurrence to vesicles
in the young topaz rhyolites that overlie the rhyolites that
contain the Be ores and occurs in association with kaolinite,
topaz, bixbyite, quartz, and manganese-iron oxides. At Wah
Wah Mountains, Utah, occurrences of late-forming red beryl,
clay minerals (primarily kaolin and mixed-layer clays), and
manganese-iron oxides are present in fractures in ≈23-Ma
topaz rhyolite. The small amounts of beryl associated with
fractures in these volcanic rocks are thought to have formed by
local redistribution of Be leached from host topaz rhyolites.
Beryllium-Fluorine Skarn-Greisen Deposits
Fluorine-beryllium deposits associated with tin deposits,
for example those of the Seward Peninsula, Alaska (Sainsbury,
1964; Alexsandrov, 2010), and the Russia Far East (Rodionov,
2000), are localized in the contact aureoles of carbonate rocks
intruded by high-silicon (leucocratic), fluorine-rich granites.
The Be is contained in veins and vugs in fluoritized and calcsilicate altered limestone and argillized granite. Beryl, helvite
group minerals, and phenakite occur along with quartz, fluorite,
topaz, tourmaline, zinnwaldite and other micas, calcite, garnet,
and sulfide minerals. Beryllium-fluorine skarn and greisen
deposits of this type are analogs of volcanogenic Be that form
in deep, high-pressure environments, and where present, may
represent the roots of volcanogenic Be systems (fig. 4).
113°10’
Map
area
Thomas Range
UTAH
THOMAS
CALDERA MARGIN
39°45’
FISH
SPRINGS
FLAT (≈5 KM)
The Dell
Spor Mountain
DUGWAY VALLEY CALDERA MARGIN
Topaz
Mountain
EXPLANATION
Quaternary alluvium
Topaz Mountain Rhyolite (6 Ma)
Spor Mountain Rhyolite (21 Ma)
Oligocene to Eocene
volcanic rocks (30–42 Ma)
0
0
3
6 KILOMETERS
3 MILES
Sedimentary rocks
Figure 4. Generalized index map showing locations of features of the Thomas Range, Utah, as referred to in
the report.
Deposit Type and Associated Commodities
Primary and Byproduct Commodities
The sole commodity produced at mines of the Spor
Mountain district is Be, and it is chiefly present as bertrandite,
although Be-bearing smectites (saponite) also occur in the
deposits. The ores at Spor Mountain average less than 1-percent BeO and are economically competitive with higher grade
beryl deposits because the volcanogenic ores are minable
by open-pit methods and can be extracted by acid-leaching
(Lindsey, 1977). Fluorite, uranium, and gem beryl have been
produced in former operations at mines in the Spor Mountain
district, generally as principal commodities rather than as
byproducts of Be mining. Volcanogenic rare metal deposits
at Brockman in Western Australia and elsewhere (see table 1)
are known to contain enrichments of Nb, REE, Ta, and Zr in
addition to Be. The metals could potentially be mined as either
byproducts (REE, Be) or primary commodities (niobium),
although none are currently being produced at that deposit or
at any others.
The BeO grades and tonnages for known volcanogenic
Be-bearing mineral deposits are shown in figure 3 along with
comparative data for Be deposits that are hosted by carbonate
sequences or pegmatites. The estimates as compiled by Barton
and Young (2002) and McLemore (2010a) are derived from
published resource estimates and geologic inventories that
reflect the sparse available data.
Example Deposits
All currently recognized volcanogenic Be deposits and
Be-rich tuffs are listed in table 1, and their general locations
are shown on figure 1. Only a limited number of deposits of
volcanogenic Be are known globally and only deposits of
the Spor Mountain district have been studied in detail. The
deposit-model attributes described below are based primarily
on published studies of current and formerly active mine sites
at Spor Mountain, which include North End, Taurus, Monitor, Roadside, Rainbow, Blue Chalk, Hogsback, and Claybank
mines (Lindsey and others, 1973, 1975; Lindsey, 1975, 1977,
1979a, 1982, 1998, 2001). Similar, although smaller, domestic
occurrences of Be minerals in tuff are present in the Honey
Comb Hills, about 30 km west of Spor Mountain (Montoya
and others, 1964; McAnulty and Levinson, 1964) and at
Apache Warm Springs, N. Mex. (McLemore, 2010a,b).
Beryllium-bearing tuffaceous rocks that have a potential to host volcanogenic Be deposits occur in a number of
regions world-wide (table 1). Beryllium tuffs of Mongolia
(Kovalenko and Yarmolyuk, 1995), such as those that occur
at Teg-Ula within the central Gobi volcanic belt, average 500
ppm Be, and their geochemical and mineralogical characteristics resemble those of Be tuff at Honey Comb Hills and low
grade ores of Spor Mountain. The Mongolian tuffs contain
clasts of rhyolite, ongorhyolite (sodium-rich), and fluorite and
are only weakly kaolinitized or unaltered. However, they are
devoid of the fluorite-opal nodules that are greatly enriched
9
in Be at Spor Mountain. Beryllium-bearing ashflow tuffs also
occur in the Macusani region of southeastern Peru (Noble and
others, 1984). The highly peraluminous rocks that compose
the Neogene Macusani volcanic field may be a northernmost
expression of the Bolivian tin belt. The tuffs contain elevated
concentrations of Be (≈15–37 ppm) and other lithophile
elements and host small occurrences of uranium and baseand (or) precious-metal-bearing minerals, but no known Be
deposits.
At the Brockman deposit in the Pilbara region of Western
Australia (Ramsden and others, 1993), a niobium-rich ashflow tuff, informally referred to as the Niobium tuff, contains
bertrandite with fluorite in late-stage calcite veins and Be is
anomalously enriched (50–1,500 ppm Be) throughout the
K-feldspar and quartz matrix. The Brockman deposit primarily
consists of low-grade lenses of Zr-Nb-Ta-REE mineralization.
The mineralization is associated with the pyroclastic eruption
of a Paleoproterozoic trachytic magma enriched in volatiles
and incompatible elements. Trace gadolinite (Be2FeY2Si2O10)
also occurs in trachyte flows that ovelie the Niobium tuff.
Deposits and occurrences of Be in Mongolia and Siberia, Russia, reportedly are hosted by fluorine-rich igneous
suites such as those typically associated with volcanogenic
Be deposits (volcanic and subvolcanic high-silica biotitebearing topaz rhyolite and granite porphyry) (fig. 2). Although
most of these deposits are hosted by granites (or subvolcanic
porphyry) and likely formed at greater pressures or depths
than tuff-related Be deposits (for example, Zabolotnaya, 1977;
Reyf, 2008; and references therein) (fig. 2), some of them have
bertrandite instead of topaz, phenakite, or beryl as the principal Be-mineral. Therefore, there may be the potential for volcanogenic Be in shallowly emplaced portions of these igneous
suites. For example, in Mongolia, the central Gobi volcanic
zone contains volcanic ongonite (topaz-bearing rhyolite),
Be-rich tuff, and REE-rich alkaline volcano-plutonic rocks
that compose part of a late Mesozoic rare metal metallogenic
belt within the Transbaikal-Mongolian rare-metal province.
However, most Siberian occurrences are hosted by Mesozoic granitoid and subvolcanic rocks and formed at greater
depths as carbonate replacement or skarn-greisen deposits
(fig. 2). For example, the Yermakovskoye fluorine-beryllium
deposit occurs in a large carbonate block (“roof sag”) within
a carbonate-terrigenous sequence preserved in a field of a preMesozoic gabbroic complex intruded by younger Mesozoic
alkali granite and leucogranite. The phenakite-microcline-fluorite ores formed at ≈224 Ma by replacement of the shattered
limestone (Lykhin and others, 2010) and have an average
grade of 1.5-percent BeO (Reyf, 2008). Another example
is the Orot bertrandite deposit—a large low-grade deposit
associated with alkaline granitoids of the Malokunalei complex and volcanic rocks of the Orot paleovolcano (Reyf and
others, 2006; Lykhin and others, 2004). The age of the Orot
volcanic edifice is 236.4 Ma and the age of granitoids (granite
or hypabyssal rhyolite) of the Malokunalei complex, which
host mineralization, is 224.8 Ma (Lykhin and others, 2004).
The Western Transbaikalian beryllium metallogenic province
10
Occurence Model for Volcanogenic Beryllium Deposits
and all known Be deposits and occurrences are thought to be
related to intracontinental rifting. The ores consist of veinlets
and replacements of dickite and bertrandite; the ore grade is
≈3,500 ppm BeO.
Metallogenic Provinces and Epochs
The global occurrence of Be-bearing tuff is generally not
restricted in age or epoch, as various deposits and potential
host rocks range in age from Paleoproterozoic to late Miocene
(table 1). Known domestic deposits and occurrences of the
class are restricted in age to topaz-bearing Tertiary-age rocks
of the Deep Creek-Tintic belt, of western Utah (Shawe, 1972),
the Trans-Pecos region of Texas (Rubin and others, 1987), and
southern New Mexico (McLemore, 2010a). Barton and Young
(2002) provide a comprehensive examination of documented
nonpegmatitic Be deposits and Be-bearing belts found worldwide. Globally, rare metal metallogenic provinces favorable
for volcanogenic Be deposits are restricted to a small number
of locations (table 1, fig. 1) where Be-bearing rhyolite or volcanic ongonite have been identified. These include Brockman,
Western Australia; Macusani, Peru; Teg-Ula, Mongolia; and
Shixi, Zhejiang, South China.
Historical Evolution of Descriptive and
Genetic Knowledge and Concepts
Barton and Young (2002) present a general classification
system for the occurrence of igneous-associated Be deposits that is based on the significant known nonpegmatitic Be
deposits and occurrences, the petrologic setting and geochemical nature of associated igneous rocks, compositional variations of intruded rock sequences, and potential metasomatic or
hydrothermal enhancement processes. Using their classification system, the Spor Mountain deposits are of the rhyolitemetasomatic-carbonate-replacement type. Aspects of the classification system of Barton and Young (2002) that illustrate
this particular deposit model and the continuum that exists
among the distinct styles of mineralization are summarized
in table 2. The generalized geologic setting for the volcanogenic Be assessment model and related Be-deposit models is
portrayed in figure 2.
The current descriptive knowledge and genetic concepts
relevant to volcanogenic epithermal Be deposits support a volcanogenic origin for metals in the host tuffs and an epithermal
origin for subsequent reconcentration into ore-grade material.
The Spor Mountain, Utah, Be deposits were discovered in
Table 2. Types of nonpegmatitic beryllium (Be) occurrences (from Barton and Young, 2002, with modifications from McLemore, 2010a,
and references both therein, unless otherwise noted). The rhyolite-carbonate type includes deposits of the volcanogenic Be and
carbonate-replacement Be models.
[1. Lists main Be-bearing phases; 2. Example localities]
Association
Type
Variety
Igneous
Magmatic
Metasomatic
Aluminosilicate
(greisen, vein)
Granite
metaluminous to
peraluminous
1. Beryl, phenakite
1. Lithium micas, beryl
2. Beauvoir, France; Shee- 2. Sherlova Gora, Russia;
Mt. Antero, Colo., U.S.A.;
prock, Utah, U.S.A.;
Boomer mine Colo.;
Pikes Peak batholith, Mt.
Aqshatau, Kazakhstan
Antero, Colo., U.S.A.;
Redskin Granite, Colo.,
U.S.A.
Rhyolite
metaluminous to
peraluminous
1. Be in glass or micas
2. Macusani, Peru; Topaz
rhyolites, Western
U.S.A. (for example,
Thomas Range, Utah)
1. Beryl
2. Wah Wah Mtns., Utah,
U.S.A.; Black Range, N.
Mex., U.S.A. (compare
Spor Mtn., Utah
Carbonate
(skarn, replacement)
1. Phenakite, chrysoberyl, bertrandite, helvite group
2. Lost River, Alaska, U.S.A.;
Mt. Wheeler, Nev., U.S.A.; Mt.
Bischoff, Australia; Victorio Mts.,
N. Mex., U.S.A. (Donahue, 2002)
1. Bertrandite
2. Spor Mtn., Utah, U.S.A.; Aguachile, Mexico (Simpkins, 1983);
Sierra Blanca, Tex., U.S.A.;
Iron Mountain, N. Mex., U.S.A.
(Nkambule, 1988)
Regional Environment
1959 using exploration methods that combined the recognition
that Be was associated with highly evolved felsic rocks and
fluorine-rich hydrothermal systems (Griffitts, 1965; Shawe,
1966) and the availability of a neutron-sourced gamma ray
spectrometer capable of rapid semiquantitative field analysis
of the Be contents of rocks (for example, Meeves 1966). Most
early exploration and assessment models for volcanogenic
Be were based on identifying Be-bearing tuffs that provided
the correct geochemical signature for such ore and local and
regional alteration patterns that might target economic mineralization (Lindsey, 1977). Recognition of textures indicative
of phreatomagmatic base surge deposits (Burt and Sheridan,
1986) was a critical factor in understanding the genesis of
the ore zones at Spor Mountain because the highly reactive
dolomite fragments in the tuff were important to localization of high-grade ore. Studies by Ludwig and others (1980)
established the presence, timing, and duration of a long-lived
hydrothermal system that is implicated in ore formation. Mineralizing processes involving both ascending magmatic-hydrothermal fluids and circulating meteoric groundwater have been
proposed to explain the origin of these Be deposits.
Regional Environment
Geotectonic Environment
Volcanogenic Be deposits are predicted to form where
there are magmatic and sedimentary source rocks of a permissive composition. The exemplar setting is an extensional tectonic environment, such as that characterized by the Basin and
Range Province of the Western United States. During the late
Cenozoic, extensive regions of western North America experienced bimodal volcanism that produced suites of basalt and
rhyolite rocks related to development of the Basin and Range
Province, including topaz-bearing igneous rock sequences
that intrude and overlie older carbonate-dominated sequences
of dolomite, quartzite, shale, and limestone (Christiansen and
Lipman, 1972). In the Western United States, topaz rhyolites
ranging in age from 50 Ma to as young as 0.06 Ma are known
to occur in as many as 30 distinct eruptive centers that formed
during periods of regional extension, lithospheric thinning,
and high heat flow (Christiansen and others, 2007, and references therein).
Topaz rhyolites associated with this deposit type have
been studied extensively in the Western United States
(Christiansen and others, 1983, 1984, 1986, 1988). They are
thought to be extrusive equivalents of anorogenic (A-type) or
residual (R-type) granitoid bodies based on their occurrence
in an extensional tectonic setting and distinctive geochemical characteristics (Burt and others, 1982; Christiansen and
others, 1983). In both bulk composition and mineralogy, topaz
rhyolites are thought to be similar to evolved parts of rapakivi
granite complexes, such as the Proterozoic complexes of
southern Finland and Latvia (Christiansen and others, 2007).
Geochemical attributes of anorogenic granites are compared to
those of topaz rhyolite in table 3. Both rock types are elevated
in REE (particularly heavy REE in the case of topaz rhyolite)
and in rare metals including Nb, Ta, Sn, Zr, and Y, and in F
and Cl. Burt and others (1982) attribute their petrogenesis to
partial melting of older continental crust in a high heat-flow
regime, which has the effect of enriching fluorine over H2O
in minerals. Related mafic magmas are thought to provide
the heat for melting and further differentiation is suggested
Table 3. Geochemical comparison of anorogenic granites and topaz rhyolites (from Burt and others, 1982;
Christiansen and others, 2007).
Feature
Anorogenic (A-type) granite1
Topaz rhyolite
fH2O
Low
Low
HF/H2O
High
High
fO2
Low to moderate
Low to moderate (near QFM)
T
High
Low to moderate (600–800oC)
SiO2
High (≈76%)
High (73–78%)
Na2O
High
Moderate-high (3–4.5%)
CaO
Low
Low (<0.8%)
REE
High, except Eu
Moderate LREE, high HREE, low Eu
Enriched
Ga, Nb, Sn, Ta, Y, Zr
Ga, Li, Nb, Rb, Sn, Ta, Th, U, Y
Depleted
Ba, Co, Cr, Eu, Ni, Sc, Sr
Ba, Co, Cr, Eu, Sc, Sr, Zr
F and Cl
High
High; F (0.3–1.5%) Cl (700–1,700 ppm)
Fe/Fe + Mg
High
High
K2O/Na2O
High
Moderate to high
After Loiselle and Wones (1979), Wones (1979), and Eby (1992).
1
11
12
Occurence Model for Volcanogenic Beryllium Deposits
to depend upon a variety of factors including (1) zone refining during ascent, (2) extreme fractional crystallization,
(3) dehydration due to early pyroclastic volcanism, and (4)
apical enrichment of near-surface magma chambers due to
liquid-state processes (Burt and others, 1982). More recently,
Christiansen and others (2007) proposed that rather than being
the melt product of midcrustal granodiorites or being derived
solely from felsic crust that either was previously dehydrated
or previously had melt extracted (as had been previously suggested), the topaz rhyolites formed by fractional crystallization of silica magmas. The silica magmas originated by small
degrees of melting of hybridized continental crust containing
a significant juvenile mantle component that was probably
derived from within-plate mafic intrusions. Christiansen
and others (2007) further note that the mafic mantle-derived
magma probably formed by decompression related to the
lithospheric extension or, perhaps, convection flow driven by
the foundering of a subducting lithospheric plate.
The volume of topaz rhyolite typically erupted from a
single volcanic vent in the Western Unites States is generally less than 10 km3; for example, the volume of the topaz
rhyolite at Honey Comb Hills in west-central Utah is 1.5 km3 .
Larger volumes of coalesced domes and magmas (as much as
50 km3) are known at Wah Wah Mountains and in the Thomas
Range in Utah (Christiansen and others, 1986) and in the
Black Range of New Mexico (Duffield and Dalrymple, 1990).
An important example is the Topaz Mountain Rhyolite, which
caps the Be-ore-bearing tuffs and lavas of the Spor Mountain
Formation (fig. 4). The felsic unit has an estimated minimum
volume of 50 km3 (Turley and Nash, 1980) and is thought to
have erupted from at least 12 distinct vent structures (Lindsey,
1979b).
Geologic Setting of Spor Mountain Deposits
Beryllium deposits of the Spor Mountain district (fig. 5)
are situated mainly along the western side of the ring fracture
of the Thomas caldera (fig. 4). The Thomas caldera was one
of a group of at least three Oligocene volcanic subsidence
structures that together form an east- to west-trending belt of
igneous rocks and related mineral deposits referred to as the
“Be belt of western Utah.”
The Thomas Range consists of three groups of volcanic
rocks that overlie a Paleozoic sedimentary sequence near
Spor Mountain (fig. 4), which is an uplifted block of multiple
faulted Paleozoic sedimentary rocks bounded on the east by
Basin and Range faulting (Lindsey, 1977; Lindsey, 1979a,b;
Lindsey and others, 1975; Shawe, 1972). The oldest group of
volcanic rocks consists mainly of latitic, andesitic, and basaltic
flows and agglomerates of late Eocene age that are exposed
along the east side of the Thomas Range. These 42–39 Ma
lava flows, breccias, and tufts of rhyodacite to quartz latite
composition were erupted from small central volcanoes and
possibly from fissures, culminating in eruption of the Mount
Laird Tuff and collapse of the Thomas caldera. Copper, gold,
and manganese mineralization accompanied the Thomas
caldera cycle. The middle group of volcanic rocks consists of
Oligocene ash-flow tuffs of quartz latite and rhyolite compositions that are well exposed in The Dell (fig. 4), an area
of ash-flow tuff that separates the Spor Mountain block from
the Thomas Range and has been interpreted as a caldera ring
fracture (Shawe, 1972). Eruption of rhyolitic Joy Tuff at
38–37 Ma was accompanied by collapse of the Dugway Valley
caldera and followed by eruption of Dell Tuff at 32 Ma. No
mineralization was associated with formation of the Dugway
Valley caldera.
The youngest group of volcanic rocks of the Thomas
Range (fig. 4; table 4) consists of alkali rhyolite tuff and flows
of the Spor Mountain Formation, which erupted at approximately 21 Ma, and the Topaz Mountain Rhyolite, which
formed at 7–6 Ma accompanying Basin and Range block faulting (Lindsey, 1979a). The Spor Mountain Formation consists
of two informal members: the lower beryllium tuff member
and an upper rhyolite lava flow member (figs. 5B and 5C; 6A
and 6B). Sanidine from the beryllium tuff member has an age
of 21.73±0.19 Ma (Adams and other, 2009). Most of the Be
mineralization at Spor Mountain is contained in the beryllium
tuff member (Staatz, 1963), which includes tuffaceous breccia,
stratified glassy tuff with clasts of sedimentary and volcanic
rocks, and thin beds of ash-flow tuff, bentonite, and epiclastic tuffaceous sandstone and conglomerate (figs. 6A and 6B).
The tuffaceous breccia and stratified tuff dominate the section
near the Be deposits but give way to bentonite and tuffaceous
sandstone and conglomerate laterally to the north and east
(Lindsey, 1979b). The breccias consist of lithic fragments with
abundant coarse, angular carbonate clasts (fig. 6C); the breccias are unsorted, laminar, and cross bedded with bomb sags.
They are interpreted as phreatomagmatic base surge deposits
because they are positioned beneath a rhyolite dome complex
next to known volcanic vents (Burt and others, 1982; Christiansen and others, 1986). The overlying rhyolite lava flow
member of the Spor Mountain Formation (fig. 6B) consists of
relatively impermeable rocks enriched in fluorine and beryllium (table 4). The younger lava flows and tuffaceous units of
the Topaz Mountain Formation form an extensive (>150 km2),
partially dissected plateau atop the Spor Mountain Formation
(fig. 4).
The chemical compositions of the Spor Mountain Formation and Topaz Mountain Rhyolite are shown in table 4.
Analyses of melt inclusions show that the concentrations of
beryllium and fluorine in quartz phenocrysts in Spor Mountain beryllium tuff and a crosscutting 21.56-Ma intrusive plug
are indistinguishable, ranging from below detection to ≈1.4
weight percent fluorine and from below detection to ≈108 ppm
beryllium (fig. 7) (Adams and others, 2009). These values are
similar to whole rock analyses of vitrophyre in the tuff and
flow (Christiansen and others, 1983, 1984; Webster and others,
1989). Thus, the median Be concentration of the melt (59 ppm,
fig. 7) is about eight times that of the clinoptilolite-potassium
feldspar altered vitric tuff (7 ppm Be, table 4).
Regional Environment
113°10'
113°15'
A
EXPLANATION
Volcanic rocks and alluvium
west of caldera margin
Rhyolite unit, porphyritic
Beryllium tuff unit, vitric
and lithic-rich
Older volcanics
×
39°45'
×
Paleozoic rocks
×
×
Beryllium deposit; surface
projection of bertranditefluorite-silica deposits in
Miocene lithic tuffs
× CLAYBANK PROSPECT
Fault
YELLOW
CHIEF
MINE
Camp
Taurus
A
South Wind
Sigma
Emma
Rhyolite vent
Fluorspar pipe
×
HOGSBACK
PROSPECT
×
Roadside
Uranium deposit
NORTH-TRENDING
FAULT SYSTEM
×
Monitor
Fluorspar vein
Fluro
Rainbow
Blue Chalk
A’
0
1
2 KILOMETERS
0
B
2000
A
Roadside
Rainbow
Blue Chalk
1 MILE
A’
1000
C
Vent, tuff
Rhyolite dome, caprock
Uranium, in tuffaceous
sandstone and
conglomerate,
disseminated and in
channels
Beryllium ore, in
lithic-rich tuff
Fluorite pipes
at depth?
Fluorite pipes
and veins
Rhyolite
Figure 5. A geologic map of Spor Mountain area, Utah, showing (A) locations and distribution of beryllium (Be) deposits
and fluorite pipes, Paleozoic carbonate rocks, the inferred boundary of the Thomas caldera, and volcanic rocks, mostly
alluvium-covered, west of faults that mark the caldera margin (fig. 4); (B) cross section (location shown in fig. 5A)
displaying the relation of the Be deposits to faults and the rhyolitic and tuffaceous host rocks; and (C) generalized cross
section of the volcanic centers and their relation to Be, fluorite, and uranium deposits. Modified from Lindsey (2001).
13
14
Occurence Model for Volcanogenic Beryllium Deposits
B
A
C
E
D
F
Figure 6. (A) Outcrop of beryllium tuff; photograph taken about 1969. (B) Roadside pit. Rhyolite caprock on right has been stripped
to expose ore in the upper part of the beryllium tuff member of Spor Mountain Formation, about 1970. (C) Monitor pit. Porous, reactive
beryllium tuff member initially composed of volcanic glass, zeolite, and abundant fragments of carbonate rock. Sample shows first stage
of alteration of dolomite to calcite. The matrix is still glassy. (D) Beryllium tuff member after mineralization is composed of a matrix of
clay and potassium feldspar; dolomite fragments are replaced by fluorite, clay, chalcedonic quartz, and manganese oxide. (E) Rainbow
pit. Ore containing nodules (relict carbonate rock clasts) of clay outlined by purple fluorite. (F) Rainbow pit. Ore containing nodules of
fluorite-dioctahedral smectite rimmed by chalcophanite. (From Lindsey, 1998).
Regional Environment
Table 4. Chemical compositions of topaz rhyolite and melt components in the vicinity of Spor Mountain beryllium district
(Christiansen and others, 1983, 1984; Lindsey and others, 1973; Lindsey, 1979a; Adams and others, 2009).
[na, not analyzed; ppm, parts per million; wt %, weight percent; Ma, million years ago]
Topaz Mountain Rhyolite, Thomas Range,
Utah
(7–6 Ma)
Topaz rhyolite vitrophyre
flow,
Spor Mountain, Utah
(21 Ma)
Unmineralized vitric tuff,
Spor Mountain, Utah
(21 Ma)
Spor Mountain
Formation (21.73±0.19 Ma)
and plug (21.56±0.07 Ma),
melt inclusions in quartz
(ppm)
Chemical composition (wt %)2
SiO2
TiO2
Al2O3
75.9
73.9
.09
12.9
.006
13.1
69 (72.9)
na (0.04)
10 (13.8)
Fe2O3
1.09
1.43
MnO
.08
0.06
1.06 (1.12)
MgO
.09
.08
.74 (0.00)
CaO
.74
1.27
1.83 (0.40)
na (0.00)
Na2O
4.11
4.33
2.78 (4.60)
K2O
4.69
3.63
4.22 (5.10)
LOI
-1
-1
5.8 (na)
H2O
1
1
4.6 (1.0)
Cl
F
-
-
1,680
.64
-
.22 (na)
1.06
.17 (1.2)
undetected to 1.4
Chemical composition (mg/kg)2
Li
40
80
75 (137)
Th
60
69
2.5 (61)
U
15
38
45 (47)
Be
6
52
7 (66)
undetected to 108
(average = 59)
Pb
na
na
Ce
129
137
34 (na)
na (194)
Analysis recalculated H2O-free by Christiansen and others (1984).
1
Data in parentheses is for SM-1, a unaltered vitrophyre chemically similar to vitrophyres of the beryllium tuff as reported by Webster and others
(1989).
2
15
16
Occurence Model for Volcanogenic Beryllium Deposits
Duration of Spor Mountain System
Range of F % by EMPA
6
Frequency
5
4
3
2
1
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Range of Be ppm by LAICPMS
12
Frequency
10
8
6
4
2
0
0
12
24
36
48
60
72
84
96 108
Figure 7. Histograms showing fluorine
(F) and beryllium (Be) contents of melt
inclusions in quartz phenocrysts from
Spor Mountain beryllium tuff and a
crosscutting 21.56-Ma intrusive plug.
Fluorine by electron microprobe analysis
(EMPA) and beryllium by laser ablation
inductively–coupled plasma mass
spectrometry (LAICPMS). Ppm, parts per
million.
Ludwig and others (1980) demonstrated that the duration of the hydrothermal (magmatic-to-meteoric) system
that included formation of the Be-mineralized nodules at
Spor Mountain was long-lived, although the Be-mineralizing
event(s) may have been episodic. They used uranium-lead isotopes of uraniferous opals from Spor Mountain to determine
both the suitability of such material for geochronologic purposes and to estimate the potential timing of uranium-, beryllium-, and fluorine-bearing minerals by proxy. They showed
that uraniferous opals can approximate a closed system for
uranium and uranium daughters making possible the dating of
opals as young as ≈1 Ma. By analyzing layers of opal intergrown with Be-bearing fluorite in nodules of the beryllium
tuff member of Spor Mountain, they showed that a hydrothermal system or systems was potentially active for a period of
almost 12 million years. In a single nodule, cores of opal and
fluorite have an age of ≈20.8 ± 1.0 Ma, essentially coeval with
volcanism. Ages of successive opaline layers decrease, clustering at ≈16 Ma and at ≈8.2 Ma. The outer opaline layers are
the approximate age of the youngest volcanic rocks present in
the region, the 7–6 Ma Topaz Mountain Rhyolite. These ages
suggest episodic periods of opal (±fluorite-beryllium) deposition, which overlap the duration of topaz-rich volcanism but
do not exclude continuous opal formation from a long-lived
hydrothermal system punctuated by influxes of magmatic,
lithophile-rich fluids. The relative importance of magmatichydrothermal fluids as a direct source of beryllium and fluorine, versus heated circulating meteoric fluids in remobilizing
beryllium and fluorine along with silica from existing glasses,
remains uncertain (see further discussion in Depositional Process section below).
Duration of the Magmatic-Hydrothermal System
and Mineralizing Processes
Relations to Structures
The timing and duration of Be ore formation spans the
interval between the time of vent-related volcanism and the
hydrothermal event(s) capable of remobilizing and concentrating Be. The hydrothermal event can be initiated as volcanism
ceases or it can be superimposed on the volcanic tuff at a later
time. For example, Be ores have the potential to form shortly
after volcanism when deposition of lithic tuff is followed
almost immediately by the development of hydrothermal
cells capable of transporting Be. The Be is then leached from
pumice, obsidian, or glass-filled vesicles. Alternatively, Be can
be associated with the direct injection of magmatic lithophiles
and precipitation of fluorite, opal, and bertrandite in replaced
clasts, veinlets, and open space. Beryllium ore formation can
continue for the duration of the magmatic-hydrothermal system,
as long as metals, heat, and fluids are available. The concentrating process for Be ore can also occur long after the magmatism
has ceased, resulting from leaching and redeposition of Be
derived from volcanic glass by heated meteoric fluids.
Basin and Range fault development influenced eruption
of the rhyolite lavas, deposition of pyroclastic surge deposits,
and movement of hydrothermal fluids in the development of
volcanogenic Be deposits at Spor Mountain district and at
Apache Warm Springs, suggesting the importance of largescale regional structures in the development of site-specific
structural aspects of volcanogenic Be deposits. At Spor
Mountain, displacements of Spor Mountain Formation and,
locally, the younger Topaz Mountain Rhyolite, demonstrate
repeated Basin and Range faulting, although some faults may
have existed prior to eruption of rhyolites. Rhyolite plugs and
domes that mark volcanic vents for Spor Mountain Formation,
as well as Topaz Mountain Rhyolite, are located along faults
and at fault intersections (fig. 5). A major north-trending fault
system related to the Thomas caldera margin (figs. 4 and 5) is
thought to have provided a regional control on mineralization
(Lindsey, 1975). A set of southwest-trending faults leading off
the north-trending fault system controlled the orientation of
tuff-filled paleovalleys. Fluorspar-cemented breccia pipes that
Physical Description of Deposit
cut the Paleozoic carbonate rocks on Spor Mountain are also
fault-controlled. At the Claybank beryllium prospect and the
Bell Hill fluorite mine, breccia and wallrock in a reactivated
margin fault are mineralized (Lindsey, 1998). The distribution
of the mineralized zones suggests that the breccia pipe systems
containing uraniferous fluorite and occurring along faults and
fault intersections acted as conduits to channel mineralizing
fluids through Paleozoic carbonate rocks (Staatz and Carr,
1964).
The Apache Warm Springs deposit, a part of the New
Mexico-Arizona beryllium belt, is located on the northeastern edge of the Mogollon-Datil volcanic field in the Sierra
Cuchillo Range. The original host lithologies were volcaniclastic rocks and rhyolite ash-flow tuffs (rhyolite of Alum
Spring). The major structures in the region are related to Basin
and Range faulting, and the mineralization is also localized in
an area of intense faulting between two major graben structures that possibly make up part of a rhyolite dome structure.
Relations to Igneous Rocks
The Be tuffs are genetically related to volcanic and hypabyssal biotite-bearing topaz rhyolites and ongonites (Kovalenko and Kovalenko, 1976; Burt and others, 1982; Christiansen and others, 1984). The regional character of the associated
igneous suites is bimodal and can consist of a broad compositional array from peraluminous to peralkaline igneous rocks,
although the immediate host volcanic rocks are typically
weakly peraluminous-metaluminous in composition and have
enrichments in Be, F, Li, Nb, REE, Th, and U (Kovalenko and
Kovalenko, 1976; Burt and others, 1982). Major provinces
of topaz-bearing rhyolite and ongonites occur in the Western
United States and the area of western Transbaikal, in Russia
and Mongolia. The general characteristics and nature of topaz
rhyolites of the Western United States have been described in
detail by Burt and others (1982) and Christiansen and others
(1983, 1984, 1986). The fluorine-rich magmas that produced
the topaz-bearing rhyolite lavas are enriched in Be, Cs, Li, Rb,
REE, Sn, Ta, Th, and U (table 3) and have been interpreted as
being derived from varying degrees of protracted or extended
differentiation (Christiansen and others, 1984). They are
widely distributed across much of the Western United States
and northern and central Mexico (Lipman and others, 1978;
Turley and Nash, 1980; Burt and others, 1982; Christiansen
and others, 1986).
Relations to Sedimentary Rocks
A critical factor in the formation of volcanogenic epithermal Be deposits is the presence of dolostone or limestone
sequences that are the source of the reactive lithic clasts in the
host tuff. At Spor Mountain, most of the Be resource occurs
as replacement of angular to subrounded, variably altered
carbonate fragments, primarily of light-gray dolomite, that
range in size from a few millimeters to more than one meter in
17
diameter. Breccia-filled volcanic pipes that cut the sedimentary
rock sequence on the eastern side of Spor Mountain (for example, Staatz and Griffitts, 1961) provided avenues for pheatomagmatic eruptions that led to the formation of volcaniclastic
surge deposits, which are high-velocity, relatively low-density,
ground-hugging turbulent fluid flows capable of transporting
lithics and ash (Burt and others, 1982). Locally, the tuffaceous
deposits contain as much as 65-percent limestone, dolostone,
and other lithics as pebbles, cobbles, and blocks, in addition to
blocks of vitric tuff (Griffitts and Rader, 1963) in a matrix of
pale-green to buff-colored volcanic ash (Shawe, 1968). Carbonate lithics are also reportedly common in pyroclastic rocks
at the Holly Claims mine, Wah Wah Mountains, Utah (Burt
and Sheridan, 1981), but are lacking in many other topaz rhyolites in Utah and throughout the Western United States (Burt
and others, 1982). For example, at Apache Warm Springs,
N. Mex., fault blocks to the south of the deposit indicate the
area is underlain by Permian marine sedimentary rocks that
include massive limestone. However, carbonate lithics are not
characteristic of the host rhyolite of Alum Spring, and the Be
minerals occur with clays in small quartz veins and stringers
and disseminations in rhyolite and ash-flow tuff.
Relations to Metamorphic Rocks
Metamorphic rocks are not genetically associated with
volcanogenic Be deposits.
Physical Description of Deposit
Deposit Dimensions
At Spor Mountain, the economic Be deposits consist of
large, lens-shaped and tabular, stratabound bodies (Shawe,
1968) that are controlled by primary volcaniclastic layering
and the original distribution of carbonate blocks and detritus
within the vitric tuffaceous unit (Lindsey, 1977). The largest
bodies of ore extend for as much as 4 km along strike over a
down-dip distance of greater than 300 m and have thicknesses
that may locally exceed 15 m. The tuff unit (fig. 6A) is as thick
as 100 m, but it is also absent locally. Within the tuff unit,
Be-rich layers range in thickness from less than 0.5 m to more
than 6 m. The length of these layers along strike and down dip
varies but can extend for more than 60 m. Weakly mineralized
rock separates some of the mineralized layers and, locally, ore
zones cut across bedding. The lateral extent of mineralization
in the district is unknown because many new discoveries may
be present on extensions of geologic structures and mineralized units that are concealed by overlying Pleistocene sediments. The surface expression of the Apache Warm Springs
deposit, which is approximately 10 × 40 m, is comparable in
size to one of the smaller individual deposits at Spor Mountain. The resource is estimated to contain ≈39,000 metric
tons and may continue beyond the known extent (McLemore,
18
Occurence Model for Volcanogenic Beryllium Deposits
2010a). Thus, economic volcanogenic Be districts are likely to
be made up of many small mineralized lenses that, as a whole,
may cover 25 square kilometers or more but individually may
cover only 100s of square meters.
Structural Setting(s) and Controls
A combination of stratigraphic and structural permeability provided pathways for mineralizing fluids to invade the
Be-bearing tuffs and react with the carbonate lithic component that was the main chemical trap for these deposits. At
Spor Mountain, fluorite-cemented breccia pipes that cut the
Paleozoic carbonate rocks (fig. 5) are fault-controlled, and
the breccia pipes served as conduits for hydrothermal fluids,
although they themselves lack appreciable Be mineralization.
As mineralizing fluids spread laterally from faults through
permeable zones in the glassy tuff, they altered and replaced
large areas of tuff, while leaving some adjacent formations
relatively unaltered. Carbonate-rich lithics were the principal trap for beryllium- and fluorine-bearing minerals. Where
hydrothermal solutions encountered zones of abundant carbonate clasts, fragments, or blocks in the tuffaceous surge deposits, they precipitated chalcedony, opaline quartz, additional
fluorite, and Be-bearing minerals. At Apache Warm Springs,
permeability in the tuff appears to have been controlled by
fine stringers and veinlets; the absence of abundant carbonate
clasts may have precluded the localization of Be in tuffaceous
lithic-rich zones.
Geophysical Characteristics
Geophysical methods used in exploration for a specific
deposit type rely primarily on the contrast of physical properties between juxtaposed formations and measure differences
in magnetic susceptibility, electrical resistivity, radioactivity, and density between the host and ore bodies. Magnetic,
gravity, and seismic data are useful in identifying large-scale
geotectonic settings and igneous suites that are associated with
volcanogenic Be deposits. For example, pronounced aeromagnetic (positive) and gravity (negative) anomalies outline the
mineral belt that extends from Deep Creek Mountains, west
of Spor Mountain, to the East Tintic Mountains in the east and
include the volcanogenic Be deposits at Spor Mountain. This
belt also contains occurrences of copper, other base metals,
and gold in addition to scattered occurrences and deposits of
fluorite and uranium (Park, 2006). The anomalies reflect, in
part, the igneous stocks and thick accumulations of volcanic
rocks that make up the calderas in the region. Aeromagnetic
contours also delineate the configuration of doming within calderas in the region; for example, the Thomas caldera contains
a central magnetic high that is thought to signify an intrusion
of resurgent magma in the core. Aeromagnetic data for the
Thomas caldera margin also reportedly show magnetic highs
of ≈2,100 gammas at the west edge of the Thomas caldera,
and the beryllium, fluorite, and uranium mines are located on
the southwest flank of the magnetic high (Shawe, 1972). The
causal relation between the deposits and the magnetic high is
unknown, but the correlation is proposed to indicate favorable
areas (Shawe, 1972). Magnetic anomalies near the Apache
Warm Springs beryllium deposit have been used to suggest
that the beryllium deposit continues south of the known extent
in Red Paint Canyon (McLemore, 2010a).
The distribution and content of key minerals including
magnetite, pyrite and other sulfides, calcite, dolomite, feldspar, and mica and clay minerals map differences in magnetic
susceptibility, radioactivity, and density that potentially could
be used to locate ore, although no examples are available for
volcanogenic Be deposits. For example, hydrothermal alteration of magnetite in mineralized tuff may produce magnetic
lows compared to surrounding volcanic rocks; the lows could
target a Be deposit within unaltered (magnetite-bearing) tuff.
Also, abundant and naturally occurring radioactive elements
(potassium, uranium, and thorium) are part of the geochemical zoning signature that targets volcanogenic Be deposits.
Elemental ratio maps prepared from gamma ray spectrometry
survey data may be useful in delineating high-grade deposits
by comparing thorium/potassium and uranium/potassium for
mineralized and unaltered tuff. Remote sensing techniques
such as advanced spaceborne thermal emission and reflection
(ASTER) and airborne visible infrared imaging spectrometer
(AVIRIS) may be useful in mapping hydrothermal alteration
minerals that have distinctive spectral features and characterize Be deposits (Rowan and Mars, 2003). The use of shortwave infrared reflectance (SWIR) spectroscopy may allow
for detailed mapping of alteration mineralogy. For example,
AVIRIS SWIR data may be used to discriminate calcite from
dolomite and identify hydroxyl-bearing clays, and as a result,
identify zones in tuff potentially more favorable for Be ore.
Hypogene Ore and Gangue
Characteristics
The Be ores that are the exemplar for this model have
been described in detail by Staatz and Griffitts (1961), Griffitts
and Rader (1963), Shawe (1968), Lindsey and others (1973),
and Lindsey (1975, 1977, 2001). The following descriptions
are based primarily on those reports, with comparisons to
other occurrences. In this context, ore zones are generally
defined as having >1,000 ppm Be in either the tuff matrix or
in nodular materials that are both clay-rich and commonly
feldspathic.
Mineralogy and Mineral Assemblages
The principal Be-bearing ore mineral associated with
deposits of this model is bertrandite (Be4Si2O7(OH)2).. The
presence of bertrandite as the sole ore mineral is consistent
with precipitation from hydrothermal fluids in a volcanogenic
Hypogene Ore and Gangue Characteristics
environment (Barton, 1986; Barton and Young, 2002 and
references therein), whereas the presence of most other Be
phases (beryl, euclase, helvite, phenakite, and bertrandite) is
indicative of formation at higher temperatures (or pressures)
not typical of epithermal environments (Barton, 1986). At temperatures above 400°C, beryl (Be3Al2(SiO3)6) is the stable Bephase. It is completely replaced by euclase (BeAlSiO4(OH))
over the range 300°C–400°C at moderate pressures. Phenakite
(Be2SiO4) is stable at temperatures greater than 250°C and
hydrates to bertrandite in the 300°C–200°C range. Bertrandite
is stable at temperatures below 250°C and, thus, indicative of
epithermal mineralization in near-surface settings.
Bertrandite is the sole Be mineral phase in volcanogenic Be deposits, although due to its fine-grain size and low
abundance (<<5 percent by weight), it is difficult to identify
by standard methods. At Apache Warm Springs, bertrandite
is found with clay in small quartz veins and stringers, along
fractures, and disseminated in the rhyolite lava and rhyolite
ash-flow tuff. Primary minerals in the original host rock are
replaced by mixtures of kaolinite, illite, quartz, hematite,
and locally illite-smectite, pyrite, anatase, alunite, pyrophyllite(?) and bertrandite. At the Honey Comb Hills occurrence,
beryllium (as much as 0.73 percent) is also associated with
submicroscopic fluorite, montmorillonite, and kaolinite in
stringers and veinlets; the Be may be present as submicroscopic bertrandite or sorbed onto mineral and or glass surfaces
(McAnulty and Levinson, 1964). At Spor Mountain, beryllium-bearing mineral assemblages occur in both stringers and
disseminations in tuff matrix and in nodules (figs. 6D, 6E, and
A
B
19
6F). The highest grade volcanogenic Be deposits consist of
abundant nodules in mineralized tuff.
The Spor Mountain Formation tuff contains pore fillings, veinlets, and nodules of opal, manganese oxide minerals,
fluorite (fig. 6E), clays (Be-bearing), and yellow secondary
uranium minerals, including weeksite (K2(UO2)2(Si2O5)3.4H2O)
and beta-uranophane (Ca(UO2)2(SiO3OH)2.5H2O). The clays
are primarily dioctahedral smectites (fig. 6F), although Bebearing smectite of the beidellite-saponite series is widespread
in layers of mineralized tuff surrounding nodules. Ore nodules
(figs. 8A, 8B, and 8C) consist of widely varying proportions
of fine-grained calcite, silica minerals, fluorite, bertrandite
(generally less than 2 percent by volume), clay, and manganese oxides. The distribution of Be in the assemblages is not
restricted to nodules, and if it is elevated in the tuff matrix,
then it is elevated in all layers in nodules, although bertrandite
only occurs admixed with the fluorite layer.
Nodules can range from a few millimeters to 30 cm in
diameter. They are typically sub-spherical in shape. Some
replaced nodules and layers display complex alteration patterns (fig. 8A), but the simplest units consist of a fairly regular
pattern of concentric and alternating zones, from core to rim,
of calcite, chalcedony, opal, and outer fluorite + bertrandite
(fig. 8B). In general, the nodules can be grouped into calcitesilica-fluorite-oxide types (fig. 8C) and fluorite-clay-manganese-oxide types (fig. 8A) (Lindsey, 1973).
Calcite and chalcedonic zones tend to be fairly monomineralic (80–90 percent). The gray-brown calcite present in
cores of nodules formed by removal of magnesium from the
C
Figure 8. (A) Nodule from Roadside pit with an interior of quartz, opal, and fluorite and an outer zone of opal
and fluorite that contains as much as 1-percent beryllium as bertrandite. (B) Nodule from Roadside pit with
an interior of gray-brown calcite, an intermediate zone of black chalcedonic quartz, and an outer zone of
white opal with minor fluorite. Beryllium is concentrated only in the outer opal-fluorite zone. (C) Fluorite-opal
nodule from Monitor prospect yielded uranium/lead ages of ≈20.8 Ma (fluorite-opal core), ≈13 Ma (white opal
middle zone), and ≈8 Ma (translucent opal rim). The ≈21-Ma age is indistinguishable from the age of the host
beryllium tuff (Ludwig and others,1980). Photographs from Lindsey (1998).
20
Occurence Model for Volcanogenic Beryllium Deposits
original dolomite clasts (fig. 9A). Remnant textures include
relict bedding, invertebrate fossil fragments, siliceous shells
and detritus, and carbonate rock textures. Electron microprobe
elemental maps (fig. 9B) demonstrate that magnesium is completely stripped from the carbonate, leaving mainly calcium
and silicon. Silica minerals include quartz, which is typically
cryptocrystalline and chalcedonic, opaline silica, and minor
smectitic clays.
Fluorite (≥50 percent) and opal are often finely intergrown in Be-rich nodules. Fluorite-opal nodules (fig. 8C)
can consist of as much as 1–2 percent Be as bertrandite but
generally average ≈100 ppm Be (Lindsey, 1973). Fluorite
ranges from purple, possibly a function of uranium content, to
colorless and is typically cryptocrystalline (<<10 micrometers
µm) grain size) and intergrown with equally fine-grained manganese oxide and silica minerals (fig. 10). Late fluorite crystals
in vugs can exceed 50 m in width and can be zoned from
colorless to purple (fig. 11A); the equant crystal form is typical
of hydrothermal fluorite (fig. 11B). Manganese oxide minerals, including pyrolusite, cryptomelane, chalcophanite, and
todorokite, occur with late fluorite and microcrystalline quartz
as rinds and fracture fillings in nodules (fig. 11A). Bertrandite is submicroscopic and finely disseminated, concentrated
mainly in the opal-fluorite stage of mineral deposition and has
only been conclusively identified in fluorite layers in nodules.
No uranium minerals have been identified in nodules, although
A
both uranium and thorium occur as anomalous trace elements
in fluorite and opaline silica.
Paragenesis
Beryllium nodules of the Spor Mountain district display a
paragenetic sequence (fig. 12) that follows a uniform pattern:
dolomite → calcite → chalcedonic quartz-opal → fluorite +
bertrandite (Lindsey, 1977). Individual nodules may show all
or part of the paragenetic sequence and monomineralic nodules are not uncommon.
The first stage in development of mineralized nodules
was the removal of magnesium from dolomite by a dedolomitization reaction (equation 1):
CaMg(CO3)2 + H2O = CaCO3 + Mg+2 + HCO3– + OH–
Calcium-carbonate and siliceous detritus remained in the nodules after the reaction. The release of magnesium and increase
in alkalinity led to deposition of trioctahedral lithium montmorillonite, producing anomalous lithium and magnesium in tuff
surrounding the ore zones.
The next stage in the paragenesis involved the replacement of carbonate clasts with successive layers of cryptocrystalline quartz or opaline silica + fluorite and beryllium. The
B
Ca
Mg
(1)
200mm
200mm
Si
F
200mm
200mm
Figure 9. (A) Siliceous shells and detritus in calcium-carbonate relic matrix being replaced by later fluorite mineralization. (B)
Elemental maps by electron microprobe analysis for calcium (Ca), silicon (Si), magnesium (Mg), and fluorine (F) confirm that
magnesium is completely stripped from the carbonate leaving a mix of mainly calcite and siliceous materials. The replacement
front is primarily microcrystalline fluorite. A patch of coarser vuggy fluorite stands out in the calcium (red) map.
Hypogene Ore and Gangue Characteristics
Ca
10 mm
Al
10 mm
21
Mn
F
10 mm
10 mm
Ce
Si
10 mm
10 mm
Figure 10. Textures typical of ore samples of volcanogenic beryllium deposits (example from Spor
Mountain district). Electron microprobe elemental maps of calcium (Ca), fluorine (F), manganese (Mn),
aluminum (Al), cerium (Ce), and silicon (Si), show typically massive fine-grained (<10 micrometers)
fluorite admixed with cerium-bearing manganese oxide and minor clay (aluminum and silicon
overlaps).
A
Dolomite
Calcite
Chalcedony
Opal
500 mm
Fluorite
Bertrandite
B
Mn-oxides
Time
50 mm
Figure 11. (A) Late fluorite and chalcedony
in vug rimmed by manganese oxide minerals.
(B) Purple fluorite and late quartz in vug.
Figure 12. Generalized paragenetic sequence for berylliumore nodules of the Spor Mountain district shows the correlation
of fluorite and bertrandite, a characteristic of volcanogenic
beryllium deposits. Compiled from Staatz and Griffitts, 1961;
Griffitts and Rader, 1963; Shawe, 1968; Lindsey and others, 1973;
Lindsey, 1975, 1977, 2001; and this study. Mn, Manganese.
22
Occurence Model for Volcanogenic Beryllium Deposits
intimate association of finely crystalline intergrowths of fluorite and bertrandite supports co-precipitation. A reaction front
showing the dissolution of calcite and precipitation of orestage minerals (fig. 9A) indicates infiltration of fluorine-bearing fluid and the wholesale replacement of calcite + siliceous
detritus by cryptocrystalline fluorite, opal, and bertrandite.
At Spor Mountain, the combination of cryptocrystalline
textures and botryoidal or colloform replacement structures
is suggestive of silica supersaturation accompanied by rapid
precipitation of opal and fluorite. Opal forms as colloidal particles of amorphous silica when a hydrothermal fluid becomes
supersaturated with respect to quartz under rapidly changing
conditions at temperatures below 200°C (Rimstidt, 1997).
In contrast, the kinetics of fluorite precipitation are such
that colloidal textures for fluorite are not usually indicative
of supersaturation (Rimstidt, 1997). Deposition of fluoritedominated ores from hydrothermal fluids can be accomplished
by a number of mechanisms including temperature or pressure
changes, fluid mixing, or as a result of wallrock interactions
(Richardson and Holland, 1979). The most likely depositional
mechanisms for fluorite associated with epithermal Be deposits of this type are wallrock reactions that cause a change in
pH and cooling of the circulating hydrothermal fluid by conduction (Wood, 1992). Fluorite formed by reaction of calcite
in nodules with a slightly acidic fluorine-bearing hydrothermal
fluid (equation 2) results in the generation of bicarbonate, an
increase in pH of the hydrothermal fluid, and the release of
Be++ from the breakdown of fluoride complexes.
Calcite + 2 F– + H+ = Fluorite + HCO3–
(2)
The formation of bertrandite (equation 3) is a function of the
general activity of silicic acid in a hydrothermal fluid, and
the precipitation of bertrandite tends to lower the pH of the
residual fluid.
4 Be++ + 2 SiO2(aq) + 5 H2O = Bertrandite + 8 H+
(3)
An overall reaction (equation 4) describing the replacement
process shown in figure 9 may be of the form
4 Calcite + 4 BeF2(aq) + 2 SiO2 + H2O = 4 Fluorite +
4 CO2(g) + Bertrandite
(4)
where BeF2(aq) stands in for the various fluoride complexes of
Be and SiO2 for the polymorphs of quartz (Wood, 1992).
Zoning Patterns
The Be ores at Spor Mountain are generally restricted
to layered, stratified tuff breccias that occur just beneath the
rhyolite lava flow member of the Spor Mountain Formation
(fig. 6B). Mineralized tuff can contain more than one discrete
Be-rich layer (Staatz and Griffitts, 1961). At most places in the
district, Be ore zones are concentrated in the upper part of the
beryllium tuff member (Lindsey, 1977). The Roadside orebody
(fig. 6) is a type locality where dolomite clasts in the upper
part of the member are mainly replaced by concentrically
zoned layers of calcite, opaline silica, and fine-grained fluorite
with submicroscopic inclusions of bertrandite. Below and outside of the ore zones, the original dolomite clasts are altered
to calcite and contain anomalous amounts of lithium, probably
in associated smectite alteration minerals. In the lowest part
of the beryllium tuff, dolomite clasts are unmineralized and
generally unaltered. Other clasts of quartzite, limestone, and
volcanic rock are relatively unaltered outside the upper part of
the beryllium tuff member. At other orebodies in the district,
Be-rich layers occur in the middle and (or) lowermost sections
of the member. For example, at the Blue Chalk deposit at Spor
Mountain, Be is found in the lowermost section near the base
of the tuff. Small mineralized zones also occur in the lower
part of the overlying topaz-bearing rhyolite of Spor Mountain
Formation.
Hydrothermal Alteration
Volcanogenic Be deposits are associated with distinctive
alteration assemblages on regional to local scales. Regionally,
Be-bearing tuffs may be extensively altered with a mineralogical signature consisting of diagenetic clays and K-feldspar. In
the vicinity of high-grade Be deposits, the tuff matrix may be
subjected to intense potassium feldspathization associated with
sericite and smectite; an assemblage that halos highly mineralized lenses and likely resulted from intense hydrothermal
alteration. Distinct geochemical signatures recognized regionally that may result from hydrothermal alteration include Be,
Cs, F, Ga, Li, Nb, and Y and in the immediate vicinity of Be
ore lenses, CaO, F, Li, and MgO may be elevated.
The bulk mineralogical and major and trace element
geochemical characteristics of hydrothermally altered and
mineralized beryllium tuff at Spor Mountain are summarized in table 5, along with data for unmineralized vitric
tuff (Lindsey and others, 1973). Beryllium, CaO, F, Li, and
MgO are elevated and montmorillonite, cristobalite + opal,
and K-feldspar are abundant in mineralized tuff compared
to relatively unaltered and unmineralized vitric tuff. At Spor
Mountain, Lindsey and others (1973) attribute all features of
the K-feldspar + montmorillonite alteration to the interaction
of circulating cooling hydrothermal fluids with a concomitant
rise in pH and decline in fluorine concentrations. However, the
deposit alteration patterns described for Spor Mountain reflect
an overprinting of hydrothermal and diagenetic processes that
are indistinguishable on the basis of currently available data.
The significance of the spatial distribution of the feldspathic
alteration, in particular, is open to question because elemental
(Be, Cs, F, Li, Ga, Nb, and Y) dispersion patterns surrounding
orebodies (described below under Zoning Patterns) reportedly
appear unrelated to K-feldspar alteration (D. Burt, Arizona
State University, written commun., 2011). Distinguishing low
Hydrothermal Alteration
temperature hydrothermal alteration caused by circulating
mixed magmatic-meteoric fluids from diagenesis caused by
burial and percolating groundwater is often difficult because
many aspects of eodiagenesis and mesodiagenesis are poorly
understood, particularly with respect to mineralogical modifications attributable to residence time, fluid chemistry, burial
depths, and mass transfer. Thus, some of the alteration assemblages described here apply to tuffs in general and may not
fingerprint Be-mineralized tuff.
Argillic and Feldspathic Alteration
The degree of pervasive alteration of tuff seen at Spor
Mountain is extremely significant in comparison to known
subeconomic occurrences and unmineralized tuff (Lindsey,
1975, 1977). Unmineralized tuff contains as much as
80-percent pumice; as much as about 14-percent primary
quartz, sanidine, plagioclase, and biotite; and trace magnetite, ilmenite, topaz, sphene, and zircon in a glassy (vitric)
or zeolitic tuff matrix. Zeolitic tuff may show alteration
patterns in a mineralogical sequence of glass + vesicular
pumice → smectite (montmorillonite clay) and matrix →
clinoptilolite. A distinctive geochemical attribute of the
altered and mineralized volcanic units is the presence of
lithium-bearing trioctahedral smectites, which closely follow and enclose Be-rich ore zones.
The intensely mineralized Be zones within the volcanic units are accompanied by alteration of the volcanic
constituents (Lindsey and others, 1973). Mineralized tuff
contains variable amounts of altered pumice, volcanic
clasts, and dolomite pebbles and as much as 20-percent
primary quartz, sanidine, plagioclase, and oxidized biotite.
Table 5. Mineralogy and chemical composition of unmineralized (vitric) and mineralized tuff, Spor Mountain and Thomas
Range, Utah. From Lindsey and others (1973).
[All values are medians. The maximum values (in parentheses) are also given where the median falls below the detection limit or where large
variation is present; mg/kg, milligrams per kilogram; -, not detected]
Alteration assemblage
Number of samples
Vitric (unmineralized)
10
Argillic (mineralized)
8
Feldspathic (mineralized)
8
Mineral composition (weight percent)
Montmorillonite1
2
Mica
Clinoptilolite
14
66
9
1
<1
<1 (40)
-
Quartz
4
5
9
Cristobalite3
3
5
25
11
18
52
Potassium feldspar4
Calcite
1
1 (23)
-
Dolomite
-
1 (5)
-
Fluorite
<3
3
4
Halite
<1
<1
1
Glass
66
<1
-
5
23
Chemical composition (weight percent)
SiO2
69
64
64
Al2O3
10
11
11
Fe2O36
1.06
1.28
1.30
MgO
0.74
1.98
1.42
CaO
1.83
2.46 (14.00)
2.90
Na2O
2.78
2.40
2.39
K2O
4.22
2.69
5.10
LOI7
5.8
8.6
5.5
CO2
0.5
0.45 (9.91)
0.06
H2O8
4.6
7.36
5.53
Cl
0.22
0.45 (1.15)
0.31 (1.75)
F
0.17
1.22
1.82
24
Occurence Model for Volcanogenic Beryllium Deposits
Table 5. Mineralogy and chemical composition of unmineralized (vitric) and mineralized tuff, Spor Mountain and Thomas
Range, Utah. From Lindsey and others (1973).—Continued
[All values are medians. The maximum values (in parentheses) are also given where the median falls below the detection limit or where large
variation is present; mg/kg, milligrams per kilogram; -, not detected]
Alteration assemblage
Vitric (unmineralized)
Number of samples
10
Argillic (mineralized)
8
Feldspathic (mineralized)
8
Chemical composition (mg/kg)
Li
Tl
75
2.5
230
3.5 (19.9)
315
6.1 (54.0)
U
45
65
85
Be
7
105
14 (250)
Cr
9
5
Cu
3
3
Fe
8,700
9,100
3 (43)
10,500
Mn
700
Ni
<7
<7 (7)
<7
Pb
34
37
42
V
14
17
11
Zn
<300
510 (3,400)
<5
<300 (340)
805 (8,000)
150 (1,600)
Dioctahedral montmorillonite clay; quantity determined by difference
1
2
Biotite plus secondary sericite
Includes some opal
3
4
Sanidine plus secondary potassium feldspar
Quantity determined by difference
5
6
Total Fe and Fe2O3
Loss on ignition (LOI) at 900ºC for 1 hour
7
LOI minus CO2
8
The alteration products include abundant montmorillonite
(both dioctahedral and trioctahedral smectites), calcite, opal,
manganese oxide minerals, feldspar, and minor kaolinite
(described below). The alteration forms a distinctive envelope
of argillized and feldspathized tuff surrounding the high-grade
deposits (Staatz 1963; Shawe, 1968). The volcanic units are
incompletely argillized, and vitric and zeolitic components
remain in mineralized tuff. Argillic tuff can contain as much
as 80 percent montmorillonite, as much as 5-percent fluorite,
and no additional feldspar, as well as fragments of fresh glassy
pumice, volcanic rock, and carbonate rock. Feldspathized tuff
represents a more advanced and complete degree of alteration.
It is identified by the presence of abundant feldspar, in excess
of unmineralized tuff, and as overgrowths of clear potassium
feldspar on volcaniclastic fragments and on sanidine. It also
includes α-cristobalite, which may have formed by recrystallization of amorphous silica by hydrothermal fluids, and as
much as 40-percent montmorillonite and 8-percent fluorite.
Kaolinitization
Kaolinitic alteration that is present near volcanogenic Be
deposits may be secondary and unrelated to mineralization
processes. Kaolinitization of volcaniclastic rocks, including
dissolution of lithics, feldspar, and mica, is common, and, in
general, the resulting spatial distributions of eogenetic kaolinite are typically related to groundwater-flow patterns at the
time of deposition or to paleotopography (for example, Morad
and others, 2000). For example, kaolinitic alteration that cuts
bedding and roughly parallels paleotopography at Spor Mountain is probably unrelated to Be ore. The widespread zeolite
and kaolinite likely formed by diagenetic alteration caused by
burial of the deposits by overlying Pleistocene sediments of
Lake Bonneville.
Supergene Ore Characteristics and
Processes
Supergene processes are not thought to be a factor in
enhancing Be ore grade. Further work is needed to fully
evaluate the importance of the observed kaolinite and zeolite assemblages (Lindsey, 1975) and identify any elemental
redistribution caused by supergene processes related to, for
example, burial conditions and the possible incursion of
Geochemical Characteristics
modified lake fluids. In the Pleistocene, the alkaline closedbasin Lake Bonneville covered much of northwestern Utah,
and at Spor Mountain, gravels, sands, silts, and indurated
marls that compose sedimentary beds of the Lake Bonneville
Group overlay the Be deposits and the youngest volcanic rock
sequences. Supergene processes acting on the tuffs are implicated in remobilization of U, F, and Mn during zeolitization
and, thus, may have overprinted some geochemical zoning
patterns related to Be mineralization. Furthermore, zeolitization is thought to have caused relative depletions in the tuff in
Na, K, F, Rb, U, Mn, and Pb.
Geochemical Characteristics
Trace Elements and Element Associations
Processes of hydrothermal alteration imparted a distinct
geochemical signature on the beryllium tuff. Anomalous
amounts of uranium (100–200 ppm) and thorium (100–150
ppm) are broadly associated with Be ore, although the anomalies may be offset from the orebodies by 10s of meters (Lindsey, 1981), possibly due to later remobilization by groundwater. For example, at the Roadside orebody, tuff immediately
underlying (within 5–10 m) Be ore contains 100–200 ppm
U, whereas the ore zone averages 50–100 ppm U. Ten to 20
m below the ore zone, uranium contents drop sharply to <25
ppm. The higher values of uranium are associated with the
abundance of a lithium-bearing smectite. In contrast to uranium, the major thorium anomaly (100–150 ppm) at the Roadside orebody is within the Be ore. Thorium levels outside the
Be ore zone are in the range of 50–100 ppm (Lindsey, 1981).
The ratio of thorium/uranium in the Be-bearing ore zone is
generally <2, whereas it rises to >4 at about 30 m beneath the
ore zone.
Zoning Patterns
An association of elements, including F, Cs, Li, Be,
Ga, Nb, and Y, compose primary dispersion halos that act as
vectors to both Be ore and fluorite deposits at Spor Mountain
(Lindsey, 1975). Other trace and minor constituents locally
enriched in the halos include manganese, zinc, and tin. Most
of the elements thought to be related to Be mineralization
form primary dispersion halos that extend as far as 3.2 km
from Spor Mountain into unaltered tuff. Thus, the geochemical
halos form a target on the order of 156 km2 that encloses the
Spor Mountain district (covering ≈52 km2). Lindsey (1975)
documented sharp declines in concentrations of cesium (from
100 to 2 ppm), lithium (from 300 to 15 ppm), and beryllium
(from >200 to <5 ppm) over a distance of 8 km from Spor
Mountain. The element dispersion patterns are distinct and
apparently unrelated to zeolitization and potassium feldspar
diagenesis of the tuffs. Thus, distinctive trace element anomalies measured in unmineralized tuff can serve as vectors to
25
volcanogenic Be ore, and the extent of the halos provides an
approximate measure for the assessment target.
Fluid-Inclusion Microthermometry
Fluid inclusion studies of volcanogenic Be deposits are
uncommon because of the fine-grained, cryptocrystalline
nature of the mineral phases. A study of atypical vuggy vein
material from the Fluoro pit at Spor Mountain did yield limited homogenization temperature data for quartz and fluorite in
the range of 143°C–163°C (Murphy, 1980). General estimates
of temperatures of formation of volcanogenic Be deposits are
between 100°C and 200°C, based on fluid data for Spor Mountain, low-temperature mineralogy (bertrandite versus phenakite), and fine-grain size (Murphy, 1980; Burt and Sheridan,
1981; this study).
Stable Isotope Geochemistry
In a preliminary study of hydrogen and oxygen isotope
signatures of unaltered rhyolite, altered rhyolite, and Be tuff
at Spor Mountain, Johnson and Ripley (1998) report evidence
for the involvement of both magmatic and meteoric waters
in alteration and ore deposition. Measured δ18O values of
unaltered porphyritic rhyolite range from 8.4 to 9.1 ‰ (parts
per thousand), whereas δ18O values for altered rhyolite are in
the range 9.3–11.7 ‰. δD values of unaltered rhyolite (–120
to –135 ‰) are lower than values typically associated with
igneous rock fully equilibrated with magmatic fluids, suggesting a model involving devolatilization and D-depletion in the
residual melt. The δ18O (9.7–11.8 ‰) and δD (–92 to –120 ‰)
values of the Be tuff define a geochemical front that requires
a model involving both magmatic fluids and meteoric waters,
suggesting that heated convecting waters leached Be and other
lithophile elements from topaz rhyolite to form deposits. A
magmatic fluid component is consistent with the introduction
of fluorine, an important criterion because fluorite is present along faults in carbonate rocks below the beryllium tuff
member.
Radiogenic Isotope Geochemistry of Ore
Compositions of nonradiogenic lead and uranium measured on opal in nodules from the beryllium tuff member of
Spor Mountain suggest that isotope data cannot be used to
distinguish volcanic units that host volcanogenic Be deposits
from unmineralized topaz rhyolite; the compositions show
no distinctive attributes that might be used to fingerprint Be
mineralization of this type. Uranium contents of opals at Spor
Mountain range from 21.8 to 1,030 ppm and lead contents
range from 1 to 129 ppm. Decay-corrected 206Pb/204Pb (17.97–
20.17) and 207Pb/204Pb (15.62–15.74) and blank-corrected
208
Pb/204Pb (38.30–39.65) values (Ludwig and others, 1980)
26
Occurence Model for Volcanogenic Beryllium Deposits
are similar to those that might be expected from the volcanic
rocks of the area as compiled by Zartman (1974).
Depositional Process
Although there is a paucity of empirical data available to
model hydrothermal fluid compositions for volcanogenic Be
deposits, some parameters can be constrained. Wood (1992)
provided a geochemical model for Spor Mountain mineralization based on an analysis of available thermodynamic
data for Be complexes and observed mineral assemblages.
The hydrothermal fluid was unlikely to have had a pH of <3,
because alteration minerals such as alunite are not present and
potassium-feldspathic alteration reactions would tend to buffer
the pH of the system at higher values. The predominance of
K-feldspar over minerals such as gibbsite and kaolinite also
suggests a limited range of K+/H+ values; muscovite-sericite
is present in only minor amounts. The activity of silicic acid
in the fluid may have been relatively low (that is, quartzsaturated) in the ascending fluid. However, during deposition,
it was likely buffered at a range of values controlled by the
presence of the abundant silica minerals (cristobalite), smectite, and volcanic glass. Beryllium may have been leached
from volcanic glass in the tuff by hydrothermal fluids during
devitrification and hydrothermal alteration. Melt inclusions in
quartz phenocrysts from a topaz rhyolite plug and Be tuff
each contain ≈59 ppm Be, whereas devitrified glass of the
Be tuff contains about 7 ppm (table 4). It is unlikely that the
mineralizing fluids contained more Be than the potential local
sources, which include devitrified glass (>7 ppm) and melts
(≈59 ppm), because the ascending magmatic fluids did not
leave an appreciable Be signature in fluorite-filled vent
structures. Thus, Be values in the range of 0.5 to 5 ppm are
reasonable for a mineralizing fluid. Wood (1992) proposed a
value of 1 ppm Be in the fluid and established that the most
feasible means of transporting Be in hydrothermal fluids
below 250°C is in complexes with fluoride. The activity of
free fluoride at mineralization sites at Spor Mountain was
likely buffered by the production of fluorite, but may have
been higher in the volcanic rock sequence if controlled by
reactions involving fluorotopaz (Wood, 1992).
A simple model illustrating a reaction path, such as the
one suggested by the replacement front shown in figure 9,
can be constructed based on the general parameters listed in
table 6. The values calculated by Wood (1992) provide for a
fluid capable of both transporting sufficient components to
the deposition site as fluoride complexes and of precipitating varying amounts of fluorite, quartz, and bertrandite. The
results (fig. 13) suggest that simple cooling of the fluid would
precipitate minor amounts of fluorite, with F– supplied by the
breakdown of aluminum-fluoride species, but not bertrandite
because the solubility of Be-fluoride species would increase
slightly with cooling as a result of declining pH. In contrast,
an isothermal (≈150ºC) or cooling fluid (≈150ºC to 100ºC)
encountering carbonate clasts would result in precipitation
of the alteration assemblages and fluorite and bertrandite in
a ratio of 100:1, which is comparable to that seen in nodules.
Clinoptilolite in the tuff would convert to amorphous silica,
muscovite, or K-feldspar, depending on changes in activity
of K+ and H+ as mineralization proceeded. This model does
not provide a unique solution because most of the intensive
parameters, including pH and temperature, are not well-constrained and the fluid composition can only be approximated
from the described assemblages.
A model hydrothermal fluid composition for Spor Mountain.
Table 6.
[Modified based on thermodynamic estimates and other data from Wood (1992)1 and Murphy (1980)2. Mg/kg, milligrams per kilogram;
ppb, parts per billion, ppm; parts per million; --, no unit]
Parameter
Unit
Fluid characteristic
Temperature
°C
200–100 ; (160–1402)
pH
--
4–6 (no alunite, K-feldspar alteration); near-neutral1
SiO2(aq)
--
Activity fixed by cristobalite
Ca, Al, K
--
Estimated by alteration assemblage of K-feldspar,
Ca-clinoptilolite, beidellite-Ca (montmorillonite), rare
sericite (muscovite)
1
HCO3
mg/kg
100
Cl
mg/kg
1,000
>0.01 molal1 or fixed by fluorite1
F
Mn
mg/kg
1
Be
mg/kg
11; (500 ppb–5 ppm)
Saturated phases
--
Bertrandite, quartz, fluorite, pyrolusite
Petrology of Associated Igneous Rocks
27
A. Cooling 150-100°C, no calcite clast
100
AlF3
10 AlF
Fluorite
1
Some species (mmolal)
10
Minerals (cm3)
Clinoptilolite-K
Amorphous silica
1
Bertrandite
145
140
135
130
125
120
115
110
105
B. Fixed temperature 150°C, react with calcite clast
Some species (mmolal = 10^-3 (milli)
moles of solute/kilogram of solvent)
Minerals (cm3)
Microcline
1
Bertrandite
Pyrolusite
5
++
++
1e–5
++
++
Be
10
15
20
150
100
Fluorite
10
0
AlF
1e–4
1e–8
100
Clinoptilolite-K
.1
.01
.001
1e–7
Temperature (° C)
100
++
-AlF22
BeF3
(aq)
BeF2
---BeF4
++
BeF
BeF
.1
1e–6
Pyrolusite
.1
150
-AlF4
--
AlF5
25
Calcite reacted (cm )
3
10
140
AlF3
1
AlF4-4-
130
120
Temperature (° C)
110
-AlF5
+
+
AlF2
.1
-BeF33
.01 BeF2 (aq)
.001
BeF
100
-BeF4
+
1e–4
++
++
AlF
1e–5
1e–6
1e–7
++
Be
1e–8
1e–9
0
5
10
15
20
25
Calcite reacted (cm3)
Figure 13. Simplified reaction paths models for the formation of fluorite replacement front in beryllium ore nodules
based on the geochemical model for the Spor Mountain district of Wood (1992). (A) Simple cooling of a hydrothermal
fluid (by conduction) from 150°C to 100°C. A small amount of fluorite is predicted to precipitate; however, bertrandite
is less stable with declining temperature. (B) Interaction of a 150°C hydrothermal fluid with carbonate clast. The
reduction of beryllium fluoride complexes in solution leads to precipitation of fluorite and bertrandite as the replacement
proceeds. Diagrams were calculated using Geochemist’s Workbench and a standard database modified with beryllium
data from Wood (1992) and the WATEQ4F database (a chemical speciation database for natural waters) from Ball and
Nordstrom (1991). Mmolal = 10-3 moles of solute/kilogram of solvent.
Petrology of Associated Igneous Rocks
Volcanic and hypabyssal high-silica rhyolite and granite
porphyry constitute the most well recognized igneous suites
associated with volcanogenic Be deposits (Christiansen and
others, 1984). The magmatic compositions of igneous rocks
associated with nonpegmatitic hydrothermal Be deposits are
invariably reported as felsic, although the general compositions can cover the range from strongly peraluminous and
metaluminous to peralkaline. Igneous systems hosting volcanogenic Be deposits, such as those found at Spor Mountain,
are metaluminous to weakly peraluminous in bulk composition. Elemental enrichments associated with these high-silica
topaz-bearing rocks include variable amounts of F, Li, Mo,
Nb, Sn, and Ta; they may contain phenakite, bertrandite, and
helvite-group minerals.
Christiansen and others (1984) described the geochemical evolution of topaz rhyolites and associated pyroclastic
deposits exposed in the Thomas Range and at Spor Mountain
in west-central Utah. The rhyolites are part of a regional late
Cenozoic bimodal sequence of basalt and rhyolite volcanism
that typified the Great Basin beginning about 22 Ma (for
example, Best and others, 1980). In general, rhyolites of the
bimodal sequence are enriched in fluorine, to as much as 1.5
percent by weight Be, Li, U, Rb, Mo, Sn, and REE. The rhyolites occur as part of a distinct assemblage of topaz-bearing
lavas that are distributed across much of the Western United
States and northern Mexico and whose general characteristics
28
Occurence Model for Volcanogenic Beryllium Deposits
are described in detail by Christiansen and others (1983,
1986). The best examples are those from the southern end of
the Thomas Range near Topaz Mountain, the type locality for
Topaz Mountain Rhyolite.
Both the Spor Mountain and Thomas Range sequences
were deposited episodically, which began with the emplacement of a series of pyroclastic breccia, flow, phreatomagmatic
base surge, and air-fall deposits and ended with eruption of
rhyolite lavas (Bikun, 1980; Burt and Sheridan, 1981). Both
volcanic rock sequences contain topaz, which is indicative
of fluorine enrichment (>0.2 percent) and have an aluminous
nature (Lindsey and others, 1973). The younger lavas and tuffaceous units of the Topaz Mountain Rhyolite were emplaced
from at least 12 eruptive centers (Lindsey, 1979b). The underlying topaz rhyolite member of Spor Mountain Formation
has an 40Ar/39Ar age of 21.56±0.07 Ma (Adams and others,
2009) and was likely emplaced from a much smaller number
of vents active at that time (Lindsey, 1982). This rhyolite and
the subjacent beryllium tuff member occurred in isolated and
tilted fault blocks on the southwestern side of Spor Mountain and as remnants of domes and lava flows on the eastern
side of the mountain. The rhyolite at Spor Mountain contains
higher concentrations of fluorine and lithophile elements
than the Topaz Mountain Rhyolite. Christiansen and others
(1984) documented the extreme enrichment in incompatible
trace elements in the lavas. They proposed that concentrations
of fluorine in the evolving Spor Mountain rhyolite (table 3)
drove residual melts to less silicic compositions with higher
sodium and aluminum and promoted extended differentiation
yielding rhyolites extremely enriched in Be, Cs, Rb, Th, and
U at moderate SiO2 concentrations (74 percent). Christiansen
and others (1984) consider that the rhyolite at Spor Mountain
may have evolved from a magma generally similar to that of
the Topaz Mountain Rhyolite, but its differentiation was more
protracted. They propose that extended fractional crystallization, possibly aided by liquid fractionation, could have led to
extreme concentrations of Be, Cs, Li, Rb, and U. Further, they
postulate that the magmatic concentrations of these elements
set the stage for the development of the Be-mineralized tuff
member, which underlies the rhyolite.
There are a number of potential mechanisms for inducing
a system to generate explosive volcanism; however, magma
mixing is the favored mechanism for the Spor Mountain Formation (Christiansen and others, 1983). The injection of hot
mafic magma into colder felsic magma can trigger vigorous
convection leading to catastrophic magmatic degassing and
explosive venting in subvolcanic plutons (for example, Sparks
and others, 1977) and extensive brecciation of and mineral
deposition in surrounding rocks (Hattori and Keith, 2001). For
example, the influx of primitive melt into the lower levels of
an upper crustal felsic magma system and subsequent mixing to produce a hybrid rhyodacitic melt may trigger volcanic
activity. Consequent decompression of the magma system
would result in the release of lithophile-bearing vapor. Large
explosive eruptions can have both magmatic and phreatomagmatic components. The presence of cross-bedded volcanic
base surge deposits preserved beneath a lava flow of topaz
rhyolite provided evidence for the involvement of magma and
water in the explosive volcanism at Spor Mountain (Burt and
Sheridan, 1981). In this case, the eruptions are presumed to
be the result of interaction between magma and water in an
aquifer. Important criteria in the recognition of the phreatomagmatic surge deposits at Spor Mountain are the presence of
coarse angular clasts, a lack of sorting, laminar bedding and
cross bedding, bomb sags, and position of the deposits beneath
a rhyolite dome complex that is adjacent to a volcanic vent.
Petrology of Associated Sedimentary
Rocks
At Spor Mountain, the thick sequence of Paleozoic
marine carbonate and clastic rocks, which provided the
carbonate lithics in the tuff, formed on a continental shelf
margin (Staatz and Griffitts, 1961). The generally conformable
sedimentary rock sequence ranges in age from Early Ordovician to Devonian, and the following description is summarized
from Shawe (1968) and Lindsey and others (1975). Limestones of the Garden City Formation, shales and quartzites
of the Swan Peak Formation, and the Fish Haven Dolomite
compose the Ordovician section. This section is overlain by
the Ordovician or Silurian Floride Member of Ely Springs
Dolomite and the Silurian Bell Hill, Harrisite, Lost Sheep,
and Thursday Members of Laketown Dolomite. The Devonian units include the Sevy Dolomite and carbonates of the
Engelmann Formation. The Ordovician section contains gray
thin-bedded limestone and tan-to-pink, weathered, mediumbedded limestone, thin beds of green shale, intraformational
conglomerate and interbedded red quartzite, thick-bedded
white vitreous quartzite, and massive black-mottled dolomite.
The Silurian section is chiefly composed of gray dolomite,
locally calcareous, which ranges from thin-bedded and finegrained to massive, dark-gray and coarse-textured sand. Some
of the Silurian dolostones contain bands of gray and (or) pink
chert, are blue-gray and mottled, and fossiliferous (Halysites).
The Devonian section consists mainly of fine-grained thin to
medium-bedded gray-laminated dolomite and local light-gray
to black limestone.
Below an elevation of ≈1,600 m, the Tertiary volcanic
rocks and the underlying and older sedimentary rock
sequences at Spor Mountain are partly covered by gravels,
sands, silts, and indurated marls of the Pleistocene to Holocene
Lake Bonneville Group. The Lake Bonneville deposits drape
up against a number of small and low foothills of sedimentary
and volcanic rocks that formed adjacent to Spor Mountain and
may conceal additional Be deposits in tuff at depth.
Theory of Deposit Formation
Petrology of Associated Metamorphic
Rocks
6.
The oldest 207Pb/235U apparent age of opal at approximately 28±1 Ma, from the opal-fluorite core of a nodule
(Ludwig and others, 1980), is essentially coeval with the
age of the rhyolite host rocks. Outer layers of uraniferous
opals yielded dates that fall into two groups at 16–13 Ma
and 9–8 Ma. Other uraniferous opals found in calcite- and
fluorite-bearing fractures in volcanic rocks as young as
6 Ma yielded ages of 5–3 Ma. This range in ages may
reflect episodic hydrothermal activity and (or) groundwater movement (Ludwig and others, 1980).
7.
Undated supergene weathering resulted in remobilization
of uranium, decoupled from thorium, and deposition of
secondary oxidized uranium beneath Be-rich zones and in
fluvial sandstones below the Spor Mountain Formation,
including potentially economic accumulations such as at
the Yellow Chief mine.
Metamorphic rocks are not genetically associated with
volcanogenic Be deposits.
Theory of Deposit Formation
Formation of volcanogenic Be deposits is due to the
coincidence of multiple factors that include an appropriate
Be-bearing source rock, thermal fluid drivers, a depositional
site, and a delivery system for concentrating the ore minerals.
Setting the framework for formation of the uniquely economic
Be mineralization was a sequence of events that are described
based on Spor Mountain. This sequence of events links critical aspects of an evolving system leading to the formation of
economic deposits of volcanogenic Be.
Sequence of Events
1.
Both the tuff and flows of the Miocene Spor Mountain
Formation contain quenched enclaves of mafic magma
(Christiansen and Venchiarutti, 1990). Injection of the hot,
volatile-rich, mafic magma into highly evolved rhyolite
magma chambers triggered eruptions.
2.
The eruption at 273±19 Ma (Adams and others, 2009)
of the beryllium tuff member of Spor Mountain Formation resulted in pyroclastic breccia, base surge, flow, and
air-fall deposits (Christiansen and others, 1984; Burt and
others, 2008).
3.
Eruption of porphyritic topaz rhyolite member of Spor
Mountain Formation occurred from at least three vents
in plugs, domes, and flows (Lindsey 1982) and included
formation of vapor-phase minerals such as topaz (Christiansen and others, 1984). Relict sanidine from an altered
plug-dome has been dated at 256±07 Ma (Adams and
others, 2009).
4.
Diagenesis of beryllium tuff member (and perhaps the base
of rhyolite flows) included formation of widespread zeolite
(clinoptilolite) ± potassium feldspar (Lindsey, 1975).
5.
Hydrothermal activity followed with deposition of
(a) fluorite, with little or no Be-bearing minerals in pipes,
veins, and faults in Paleozoic carbonate and Oligocene
volcanic rocks below the beryllium tuff member at Spor
Mountain; (b) disseminated deposits of fluorite that
are Be-bearing in rhyodacite, rhyolite, and tuff; and (c)
concentrations of bertrandite, amorphous silica (opal),
fluorite, clay minerals (hectorite), and potassium feldspar
in the beryllium tuff, particularly at the former sites of
lithic fragments of dolomite (Lindsey, 1977).
29
Genetic Model
A genetic model that illustrates the development of stages
of mineralization for volcanogenic epithermal Be deposits
constructed by Burt and Sheridan (1981) is shown in figure 14.
The stages described below relate the sequence of events to
the components and processes of mineralization:
Stage 1—Igneous source: High-silica, lithophile-rich
magmas capable of producing volcanic and hypabyssal highsilica biotite-bearing topaz rhyolite and granite porphyry compose the source material. Barton and Young (2002) calculated
that a small amount of a hypothetical Be-bearing magma (0.4
km3 at 3.6 ppm Be) would be required to make a world-class
deposit such as Spor Mountain (see fig. 1). They compared
that with the 100 km3 or more that is required for most metals
in most other deposit types. However, the much higher median
concentration of Be (59 ppm) in melt inclusions measured
for Spor Mountain (Adams and others, 2009) suggests that an
even smaller minimum volume of magma (0.135 km3) or tuff
(0.272 km3) is required to provide sufficient Be (fig. 15). If Be
was derived solely from tuff, then a block 1 km wide × 5 km
long × 54 m thick is required to account for the Be ore in the
district. These calculations for minimum volumes of rock necessary to form such a deposit assume extraction efficiencies
of 100 percent. Lower extraction efficiencies would require
substantially larger volumes of rock (fig. 16). The low average
concentration of 7 ppm Be in the clinoptilite- and adulariaaltered vitric tuff at Spor Mountain compared to melt inclusions (average ≈59 ppm) and unaltered vitrophyre (66 ppm)
suggests an extraction efficiency on the order of 90 percent
for the glassy matrix. Thus, a substantial amount of Be was
potentially leached from the estimated 10 km3 of tuff erupted
in the region (Lindsey, 1982).
Stage 2a—Driver: A mechanism is required that would
result in explosive lithophile-rich rhyolite volcanism and vigorous convection leading to catastrophic magmatic degassing
and explosive venting in subvolcanic plutonic systems, the
30
Occurence Model for Volcanogenic Beryllium Deposits
STAGE 1: Intrusion of magma
STAGE 2A: Eruption of pyroclastics
Gas cloud pyroclastics
Lithic
fragments
Carbonate
Aquifer
Stagnant zone
enriched in volatiles
and lithophile
elements
Chilled
margin
Convecting
zone
STAGE 3: Mineralization resulting from near-surface convection
STAGE 2B: Eruption of dome-flow complex
Rhyolite dome
Sn
Tuffs
Be, Li, U
Flow
F
F
Mo,W?
Figure 14. A general model for formation of volcanogenic deposits of uranium (U), beryllium (Be), and other lithophile elements as
proposed by Burt and Sheridan (1981). Sn, tin; Li, lithium; F, fluorine; Mo, molybdenum; W, tungsten.
release of lithophile-bearing magmatic vapor phases from the
felsic magma, and the potential for forming carbonate clastrich volcanic surge deposits in tuff. Christiansen and others
(1984) proposed that magma mixing in the chamber is an
effective mechanism for generating the catastrophic degassing and venting. They consider that the fluorophile element
(for example, Be, Cs, Li, U, and Rb) enrichments in the Spor
Mountain rhyolite magma resulted from extended fractional
crystallization aided by liquid fractionation. The Be-bearing
glasses in the tuff contribute geochemical and mineralogical
components to hydrothermal fluids.
Stage 2a—Site: Basin and Range fault development influenced eruption of the rhyolite lavas, deposition of pyroclastic
surge deposits, and the movement of hydrothermal fluids in
the Spor Mountain district. High-angle fault systems within
the district provided regional controls on mineralization and
pipes. Faults through the underlying carbonate rocks acted as
conduits to channel mineralizing fluids to the Be-bearing tuff.
Breccia-filled volcanic pipes that cut the underlying sedimentary rock sequence signal the explosive volcanism that
generated carbonate lithic-rich phreatomagmatic base surge
deposits. The pipes provided avenues for magmatic fluids to
Theory of Deposit Formation
B. A beryllium pluton (≈59 ppm Be)
A. A beryllium tuff (≈59 ppm Be)
Minimum volume of pluton
≈135 million m3
Minimum volume of beryllium tuff ≈272 million m3
density≈2.6 g/cc
512 m
512 m
C. Estimated volume of Be ore (≈2,570 ppm Be)
≈4.36 million m3
density≈1.85 g/cc
500 m
500 m
54.3 m thick
8.73 m
thick
density≈1.47 g/cc
100 m
1,000 m
Figure 15. Minimum volumes of tuff or pluton required to form beryllium (Be) resource at Spor Mountain. (A). Volume of tuff
(272 million m3, d (density) =1.47 gram/cubic centimeter (g/cc); corrected for presence of phenocrysts and carbonate in tuff; 59
parts per million (ppm) Be that must be completely leached of Be to form the ore corresponds to a block (shown as stack of 10
slabs) 54.3 m thick, 1 km wide, and 0.5 km long. This volume makes models that call upon mobilization of Be from altered tuff
permissive. (B). Volume of pluton required to account for amount of Be in ore is smaller than amount of tuff because its density
is higher (2.6 g/cc, 135 million m3). This corresponds to a cube about 0.5 km on a side, which is similar in size to cupolas that form
important porphyry deposits. Thus, models that call upon release of volatiles from cooling plutons also are permissive.
(C). Relative volume of Be ore (4.36 million m3, d=1.85 g/cc, 2,570 ppm Be) is shown in ten stacked bodies 500 m × 100 m × 8.75 m.
These bodies are comparable in dimension to some of the larger individual ore lenses of Spor Mountain (for example, see fig. 3).
3,000
Million m3
2,500
2,000
tuff
1,500
1,000
pluton
500
0
100
75
50
25
Percent extraction efficiency
10
Figure 16. Plot showing extraction efficiency
(percent) versus volume (million m3).
31
32
Occurence Model for Volcanogenic Beryllium Deposits
reach and interact with meteoric fluids and eventually generate
the hydrothermal cells capable of leaching Be from volcanic
glass in the tuff. At the depositional site, carbonate lithics and
ignimbritic textures of the tuff supplied both porosity and
permeability, and Be-bearing glasses in the tuff contributed
geochemical and mineralogical components.
Stage 2b—Confined system: The position of the Be
tuff between relatively impermeable Paleozoic rocks and a
younger topaz rhyolite lava flow confined circulating hydrothermal fluids to the porous and permeable tuffaceous breccias
and stratified vitric tuff. This set the stage for focused, potentially long-lived hydrothermal fluid flow through the tuff.
Stage 3—Delivery system: Leaching of large volumes of
lithophile-rich volcanic source rock by a large-scale hydrothermal system can provide the beryllium, fluorine, and other
lithophile elements that characterize the ores. At Spor Mountain, hydrothermal leaching of the Be tuff led to deposit formation; however, the role of shallow degassing of magma, with
or without deep Be mineralization, cannot be excluded (Wood,
1992; Barton and Young, 2002). Mineralization processes
involving both magmatic fluids (Staatz and Griffitts, 1961;
Shawe, 1968; Lindsey and others, 1973) and heated meteoric
fluids (Burt and Sheridan, 1981) have been proposed, but the
relative roles of Be introduction by ascending magmatic fluids
versus leaching of Be from volcanic glass by circulating shallow heated meteoric groundwater remain uncertain.
Stage 3—Trap: A vital factor in development of the
depositional trap for the richest Be ore was the incorporation
of dolomite as lithic fragments in volcanic surge deposits,
which formed as a result of explosive phreatomagmatic eruptions (Burt and Sheridan 1981). The highly reactive dolomitic
fragments encased in tuff were subsequently mineralized by
interaction with fluorine- and beryllium-bearing hydrothermal
fluids, and the replaced fragments now form beryllium-rich
nodules.
Formation of the mineralized nodules has two distinct
aspects. Initially dolomite fragments are converted to calcite by removal of magnesium, and, subsequently, calcite is
replaced by successive layers of rhythmically banded chalcedonic quartz and opal and fine-grained bertrandite-bearing
fluorite. Thus, the overall hydrothermal process involves a
combination of dissociation, dissolution, and precipitation.
The conversion of dolomite to calcite caused subsequent
precipitation of magnesium smectites. Mineralization proceeded with dissolution of calcite and precipitation of varying forms of silica, fluorite, and bertrandite. The proposed
mechanism for precipitation (Lindsey and others, 1973;
Lindsey, 1977; Wood, 1992) is the declining fluorine activity
as cooling hydrothermal fluids encountered carbonate in the
tuff. Changes in pH and temperature of the fluid are factors in
fluorite precipitation. Bertrandite precipitation is favored by
loss of the fluoride ligand during precipitation of fluorite, as
well as the associated changes in pH and activity of silica.
Geoenvironmental Features and
Anthropogenic Mining Effects
The uniqueness of the Spor Mountain Be deposit and
its location in a fairly arid climate have limited the amount
of geoenvironmental information available for volcanogenic
Be deposits. Despite the paucity of information, meaningful insights into the geoenvironmental characteristics of this
deposit type can be gained from its geologic characteristics
viewed in the context of relevant regulatory guidance. Key
features of Spor Mountain-type Be deposits that relate directly
to their geoenvironmental characteristics include association
with high-silica rhyolites; replacement of carbonate rocks;
presence of bertrandite (Be4Si2O7(OH)2) as the main ore
mineral, with silica, calcite, fluorite, potassium feldspar, and
clays; association with fluorine and uranium enrichments; and
sulfide-poor character (Lindsey and others, 1973; Lindsey,
1977; Barton and Young, 2002). Collectively, these features
contribute to a deposit type for which minimal environmental
concerns are present.
Weathering Processes
From an environmental perspective, weathering processes associated with mine wastes from processing ore are
dominated by the weathering of remnant bertrandite, fluorite,
and uranium-bearing minerals from a mineralogically poorly
defined source. Lindsey (1981) speculated that uranium at
Spor Mountain is hosted by uraniferous fluorite or opal. Bertrandite, the primary ore mineral, presumably occurs in mine
waste in minor amounts due to imperfect grinding of ore prior
to ore processing.
The environmental geochemistry of Be deposits and their
associated mine wastes has been the subject of few studies
(Deubner and others, 2001; Stefaniak and others, 2008). More
general information is also available on Be in the environment
(Veselý and others, 2002; Taylor and others, 2003).
Most of the environmental concerns associated with Be
deposits focus on airborne particles associated with ore and
metallurgical processing (Deubner and others, 2001; Stefaniak
and others, 2008). Nevertheless, the dissolution of bertrandite
can be described by the reaction
Be4Si2O7(OH)2 + 8 H+ → 4 Be2+ + 2 H4SiO4 + H2O(
5)
or the reaction
Be4Si2O7(OH)2 + 8 H+ → 4 Be2+ + 2 SiO2 + 5 H2O
(6)
in the presence of quartz or amorphous silica (Wood, 1992).
The solubility of Be is expected to be extremely low (<1 μg/L),
except under low pH (<3.5) conditions (fig. 17). Due to the
lack of sulfide minerals to generate acid and the abundance of
limestone at Spor Mountain, low pH conditions are unlikely
Geoenvironmental Features and Anthropogenic Mining Effects
maximum concentration of 4.0 milligrams per liter (mg/L) in
one sample located more than 30 km from the mine. Groundwater samples nearer the mine site had fluoride concentrations
of 0.4 to 2.9 mg/L (table 7). For comparison, the maximum
contaminant level for drinking water is 4 mg/L (table 8).
In the absence of site-specific data for volcanogenic Be
deposits, Be concentrations in average crustal rocks and soils
offer a useful reference in the absence of baseline data from
unmined deposits. The average upper crustal abundance of
Be is 3.1 milligrams per kilogram (mg/kg). Concentrations in
soils range from 0.1 to 300 mg/kg with a global average of 6
mg/kg (Veselý and others, 2002). However, global values of
Be in soils are thought to be high in comparison to soils in the
United States, and soils and regolith of the arid western States
of Utah and New Mexico have Be contents of generally less
than 1.5 ppm (Shacklette and Boerngen, 1984).
0
25°C
–2
–4
Bertrandite
log a Be2+
–6
–8
–10
Be2+
–12
Be(OH)3-
BeOH+
–14
0
2
4
6
pH
Be(OH)2(aq)
8
10
12
33
14
Figure 17. Diagram showing the solubility of bertrandite and the
dominant speciation of dissolved beryllium (Be) as a function of
log aBe2+ and pH at 25°C. The activity of silica was buffered by the
presence of quartz in the calculations. Diagram was calculated
using the Geochemist’s Workbench using the data from Wood
(1992) and WATEQ4F (a chemical speciation database for natural
waters) from Ball and Nordstrom (1991).
associated with the deposit. However, the Be extraction
process from bertrandite ores involves acid leaching at high
temperature using sulfuric acid (Stonehouse, 1986). Thus,
such ore-processing practices could potentially lead to Be
discharge to surface water and groundwater in the vicinity of
the ore-processing facility.
Pre-Mining Baseline Signatures in Soil,
Sediment, and Water
Pre-mining baseline geochemical data surrounding the
Spor Mountain deposits are essentially lacking. Bolke and
Sumsion (1978) conducted a reconnaissance hydrologic study
in the Fish Springs Flat area, covering an area of 27 × 56 km
in Tooele, Juab, and Millard Counties, Utah, which includes
the Spor Mountain mine. Precipitation averages 18 cm per
year. Stream flow is ephemeral and mainly due to thunderstorms or snowmelt. The more widespread regional dataset
indicates that groundwater in the Fish Springs Flat area is
neutral to slightly alkaline (pH 7.2 to 8.0) and is characterized as being slightly saline to briny (specific conductance
2.89 to 34.70 millisiemens per centimeter). The only element
of environmental concern included in the analyses presented
by Bolke and Sumison (1978) was fluoride, which reached a
Past and Future Mining Methods and Ore
Treatment
Ores at Spor Mountain are mined by open-pit methods.
The sheet-like ore zone ranges between 0.6 and 12 m in thickness (Hawkins, 2001). The ores undergo a series of crushing
and chemical extraction steps to produce either a Be-carbonate
(BeCO3) or Be-hydroxide (Be(OH)2) product (Stonehouse,
1986). The crushed ores are ground to less than 20 mesh.
The resulting slurry is leached with sulfuric acid at elevated
temperature resulting in an aqueous solution containing
approximately 0.7 grams per liter (g/L) beryllium, 4 to 7 g/L
aluminum, 3 to 5 g/L magnesium, and 1.5 g/L iron. Further
processing strips the Be from this solution.
Volume of Mine Waste and Tailings
The ore at Spor Mountain averages 0.3-percent Be (0.72
weight percent BeO) with a total tonnage of approximately
7 Mt (Lindsey, 2001). Mining occurs with a stripping ratio
(waste rock:ore) of 23:1 (Hawkins, 2001). Because of the low
grade of the ore, essentially all of the mined and processed ore
becomes waste.
Mine Waste Characteristics
Chemistry
Due to the low concentration of Be in the ore, the geochemistry of the mineralized tuff should be representative
of most of the bulk geochemical characteristics of the waste
material. The geochemical characteristics of the mineralized
tuff at Spor Mountain have been summarized by Lindsey and
others (1973). The data, summarized in table 5, come from
both argillically and feldspathically altered mineralized tuffs,
which contain some carbonate clasts. For the most part, the
major-element data reflect the rhyolitic protolith (Si> Al> K>
34
Occurence Model for Volcanogenic Beryllium Deposits
Table 7. Geochemical characteristics (dissolved) of groundwater in the vicinity of the Spor Mountain deposit, Utah.
From Bolke and Sumsion (1978).
[mS/cm, millisiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; --, no value]
Parameter
Mine site1
(C-13-12)5cbd-1
Unit
Nearby1, 2
(C-12-12)10cbc-S1
(C-14-12)4cbc-1
Temperature
°C
16.5
pH
--
--
7.3
--
2.89
8.40
4.05
Specific conductance
mS/cm
SiO2
mg/L
Ca
mg/L
22.0
3.2
130
23.0
31
52
690
110
Mg
mg/L
53
170
72
Na
mg/L
410
870
650
K
mg/L
HCO3
mg/L
180
SO4
mg/L
340
380
300
Cl
mg/L
610
2,500
980
F
mg/L
5.1
0.6
18
23
227
360
2.9
0.40
Fe
μg/L
150
120
20
Mn
μg/L
20
100
10
B
μg/L
320
490
1,100
The groundwater temperatures are higher than expected for nonthermal groundwater in the area; the total range reported by Bolke and Sumsion (1978) for the area is from 16.5°C to 60.5°C and includes data for hot springs. The paucity of field measurements for the dataset precludes
normalizing for temperature or effects.
1
Nearby samples are located within 15 km of the mine site.
2
Table 8.
Environmental guidelines relevant to Spor Mountain Be deposits.
[Criterion: LOEL, lowest observable effects level; TLV, threshold level value. Sources: CCME, Canadian Council of Ministers of the
Environment; NIOSH, National Institute of Occupational Safety and Health; USEPA, United States Environmental Protection
Agency; WHO, World Health Organization. Mg/L, micrograms per liter; mg/kg, milligrams per kilogram; mg/m3, micrograms per
cubic meter; --, no value]
Medium/criterion
Units
Beryllium
Fluorine
Uranium
Source
Human health
Drinking water
mg/L
4
4,000
--
USEPA (2009)
mg/L
50
1,500
15
WHO (2008)
mg/L
--
1,500
20
CCME (2010)
Residential soil
mg/kg
160
--
230
USEPA (2009)
mg/kg
--
--
23
CCME (2007)
Industrial soil
mg/kg
2,000
--
3,100
USEPA (2009)
mg/kg
--
--
300
CCME (2007)
2,500
200
NIOSH (2005)
--
--
USEPA (1980)
--
--
USEPA (1980)
Air (TLV)
3
mg/m
2
Aquatic ecosystem health
Surface water acute (LOEL)
mg/L
Surface water chronic (LOEL)
mg/L
130
5.3
Geoenvironmental Features and Anthropogenic Mining Effects
Ca ≈ Na> Fe ≈ Mg). The trace-element data show notable
enrichments in beryllium, fluorine, and uranium relative to
unmineralized counterparts.
Mineralogy
The mineralogical characteristics of the mineralized tuff
at Spor Mountain have also been summarized by Lindsey and
others (1973). The data, also summarized in table 5, come
from both argillically and feldspathically altered mineralized
tuffs, which contain some carbonate clasts. The mineralogy is dominated by clays, potassium feldspar, quartz, and
cristobalite. Calcite and dolomite clasts are locally important.
Fluorite is locally abundant in the ore assemblages and bertrandite is an important trace mineral. Uranium does not form
discrete phases but instead is probably bound in fluorite and
opal (Lindsey, 1981).
Acid-Base Accounting
Acid-base accounting data are lacking for the Spor
Mountain deposit. Nevertheless, the lack of sulfide minerals
and the presence of carbonate minerals as clasts suggest that
the waste material should be net-alkaline in character.
Element Mobility Related to Mining in
Groundwater and Surface Water
The only site-specific data for groundwater associated
with a Spor Mountain-type deposit are the results of Bolke and
Sumsion (1978) from the lone well sampled at the site in 1977,
roughly eight years after the start of mining. The well was
within the rhyolite and reached a depth of approximately 190
m. The geochemical characteristics of the groundwater at the
mine site are compared to other groundwater samples in the
study area in table 7. The pH was not measured at the time of
sampling, but the major-element chemistry, including fluoride
concentrations, was similar to that of the regional groundwater
sampled at two sites within 10 km of the mine (table 7).
Ecosystem Issues
Ecosystem issues related to mining are unlikely in the
vicinity of the Spor Mountain deposits because of the arid
climate, lack of surface water, and the low concentrations of
beryllium and uranium in the ores. Water-quality criteria for
beryllium are currently lacking in the United States. However, USEPA (1980) does provide lowest observable effects
limits as guidance for acute and chronic toxicity to aquatic
life for Be of 130 and 5.3 μg/L, respectively. Water hardness
is reported to have a significant effect on the acute toxicity of
Be (USEPA, 1980). In contrast, LeBlanc (1980) determined
lethal concentrations for 50 percent of test organisms (LC50)
for Daphnia magna of 1,900 μg/L for 24-hour exposures, and
35
1,000 μg/L for 48-hour exposures in test water with a hardness
of 173 mg/L CaCO3 and pH 8. Jagoe and others (1993) found
acute toxicity (mortality) to juvenile perch (Perca fluviatlis)
at dissolved Be concentrations greater than 10 μg/L at pH 4.5
and greater than 50 μg/L at pH 5.5; concentrations greater
than 100 μg/L were lethal to juvenile roach (Rutilus rutilus)
regardless of pH. Relative to bertrandite solubility, these concentrations would only be expected below a pH of 3 (fig. 17).
Sediment guidelines are lacking for Be.
The ecological toxicity of Be in soils has been assessed
by Kuperman and others (2006) who investigated chronic
effects on soil invertebrates, such as earthworms, potworms,
and collembola by dose-response assessment methods. Their
lowest measured value of no-observed-effect concentration
was 18 mg/kg, and their lowest lowest-observed-effect concentration for a survival endpoint was 24 mg/kg. Their lowest
value of no-observed-effect concentration for a reproduction
endpoint was 24 mg/kg, and their lowest value of lowestobserved-effect concentration was 36 mg/kg.
Human Health Issues
Human health concerns associated with Spor Mountaintype Be deposits and their wastes center around airborne particulates at ore-processing facilities. Beryllium concentrations
in excess of the drinking water standard (4 μg/L; table 8) are
unlikely due to the low solubility of bertrandite (fig. 17).
Several studies have investigated Be toxicity associated
with the mining and milling of ores at Spor Mountain (Deubner and others, 2001; Stefaniak and others, 2008). In addition,
a review of the health effects of Be was conducted by the
U.S. National Research Council (2007). A major concern is
“chronic Be disease,” which is a debilitating and potentially
lethal lung disease, and its precursor, Be sensitization, an
immune system disorder, both of which are most commonly
described from the nuclear weapons and Be manufacturing
industries via an inhalation pathway (Kreiss and others, 2007).
Also, the United States Environmental Protection Agency
classifies Be as a likely human carcinogen (U.S. National
Research Council, 2007). Neither Be sensitization nor chronic
Be disease have been diagnosed in miners at Spor Mountain
(Deubner and others, 2001), which is consistent with the low
Be concentrations of the ores being mined. Deubner and others (2001) found median breathing zone and lapel air-sample
concentrations associated with mining and milling at Spor
Mountain to be less than 0.8 micrograms per cubic meter (μg/
m3) over their monitoring period from 1971 to 1999, compared
to the threshold level value of 2 μg/m3 (table 9). They also
suggested that the speciation of Be in solid form may affect
its toxicity, with bertrandite, beryl, and Be salts posing lower
risks than Be hydroxide.
36
Occurence Model for Volcanogenic Beryllium Deposits
Climate Effects on Geoenvironmental Signatures
canogenic Be deposits. Alteration processes related to
Be-mineralization can be expected to result in widespread
and pervasive hydrothermal alteration haloes of smectite,
sericite, and potassium feldspar. The presence of abundant trioctahedral lithium smectite, which forms early as
magnesium becomes available from alteration of dolomite
and as Li, Zn, U, Th, and Mn are supplied by mineralizing
solutions, is a particularly favorable indicator.
Studies related to climatic effects on geoenvironmental
signatures on volcanogenic Be deposits are lacking. Nevertheless, the absence of significant secondary Be salts, the low
solubility of bertrandite and fluorite, and the low but significant
concentrations of uranium associated with the ores suggest that
climatic variations should not greatly influence the geochemical behavior of Be or associated fluorine and uranium.
6.
Anomalous concentrations of Be, Ce, F, Ga, Li, Nb, and
Y in otherwise unaltered volcanic rocks may also indicate
favorability for volcanogenic Be deposits. These elements
define primary dispersion halos that act as vectors to Be
ore. Geochemical halos may extend as far as 3–4 km into
unaltered tuff. Thus, the halos form a target on the order
of 156 km2 that may be expected to enclose volcanogenic
Be deposits covering ≈52 km2
7.
Economic volcanogenic Be districts are likely to be made
up of many small mineralized lenses that, as a whole, may
cover 50 km2 or more, but that individually may cover
only 100s of square meters.
Exploration and Resource Assessment
Guides
1.
2.
3.
4.
5.
Rhyolitic rocks rich in fluorine, beryllium, tin, and other
lithophile metals are the favorable volcanic-magmatic
source for these deposits. Beryllium tuffs are genetically
related to volcanic and hypabyssal biotite-bearing topaz
rhyolites and ongonites. The regional character of the
associated igneous suites is bimodal and can consist of a
broad compositional array from peraluminous to peralkaline igneous rocks, although the immediate host volcanic
rocks are typically weakly peraluminous to metaluminous
in composition. In the Western United States, these rocks
are mostly plugs, domes, flows, and tuffs of Tertiary
topaz-bearing rhyolite.
Deep fractures, such as margin faults and caldera ring
fractures related to extensional tectonics, are instrumental
in tapping the sources of rhyolitic magma and lithophilerich mineralizing fluids. The process of magma mixing is
thought to provide the primary mechanism for explosive
volcanism, as is supported by geochemical attributes of
the volcanic system, mafic inclusions, vent structures, and
volcaniclastic surge deposits.
Porous carbonate-bearing tuffs and vitric volcaniclastic
rocks are favorable hosts for volcanogenic Be deposits.
The reactive carbonate minerals may occur as lithic fragments, veins, and (or) disseminations in tuff. The richest
Be ore zones may be associated with mineralized carbonate lithic-rich phreatomagmatic base surge deposits, or
other carbonate lithic-rich volcanic units. Adjacent breccia
zones in carbonate rocks may also provide suitable host
rocks for localized deposits.
Fluorspar and uranium deposits indicate the presence of
lithophile-rich mineralizing hydrothermal fluids capable
of transporting economic amounts of Be. General estimates of temperatures of formation of volcanogenic Be
deposits are between 100°C and 200°C based on fluid
data, low-temperature mineralogy (bertrandite versus
phenakite), and cryptocrystalline grain size.
A distinctive association of hydrothermal alteration
minerals is a favorable indicator of proximity to vol-
Acknowledgments
Chemical analyses of melt inclusions were conducted in
the Denver Inclusion Analysis Lab (DIAL) by David Adams,
Todor Todorov, and Erin Marsh. The 40Ar-39Ar analyses on
sanidine and resulting isotopic dates were conducted by Mike
Cosca and John Lee. The report has benefitted greatly from
constructive and thoughtful reviews by Virginia McLemore
(New Mexico Bureau of Geology and Mineral Resources),
Donald Burt (Arizona State University), and Richard Goldfarb
(U.S. Geological Survey).
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43
Foley and others—Occurrence Model for Volcanogenic Beryllium Deposits—Scientific Investigation Report 2010–5070–F